X-ray mask, method of manufacturing the same, and X-ray exposure method

ABSTRACT

In an X-ray exposure method of this invention, an X-ray mask unit in which a patterned X-ray absorber is formed on a membrane is supported. This patterned X-ray absorber contains one of an element having a density/atomic weight of 0.085 [g/cm 3 ] or more and an L-shell absorption edge at a wavelength of 0.75 to 1.6 nm and an element having a density/atomic weight of 0.04 [g/cm 3 ] or more and an M-shell absorption edge at a wavelength of 0.75 to 1.6 nm. Synchrotron radiation having maximum light intensity at a wavelength of 0.6 to 1 nm is applied onto the X-ray mask unit. This improves the exposure accuracy in X-ray exposure.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an X-ray mask suited to proximity X-raylithography for use in semiconductor production, a method ofmanufacturing the same, and an X-ray exposure method.

2. Discussion of the Background

With the recent shrink in feature size of semiconductor integratedcircuits, a proximity X-ray lithography exposure method by which a maskand a wafer substrate are placed close to each other and mask patternsare transferred onto the wafer substrate by using X-rays having a shortwavelength has been proposed.

A suitable wavelength region of a light source used in actual proximityX-ray lithography is determined by Fresnel diffraction controlling theresolution of the transfer pattern and the secondary electrons generatedin the substrate by X-rays. The narrower the gap between the mask andthe wafer and the shorter the exposure wavelength, the smaller thediffraction of light and the higher the resolution. On the other hand,the secondary electrons such as photoelectrons and associated Augerelectrons increase and affect the exposure in a resist whenshort-wavelength X-rays are used in exposure, and these secondaryelectrons lower the resolution. From the relationship between thesediffraction effect and secondary electron effect, therefore, theexposure wavelength of X-rays used is preferably 0.6 to 1 nm in terms ofresolution, so it is desirable to use X-rays of 0.6 to 1 nm in exposure.

In actual exposure system and conventional X-ray masks, however, anabsorber material of the masks suited principally to one specificwavelength is assumed. Therefore, no examinations have been done for anabsorber and an X-ray mask suitable for synchrotron radiation having awavelength region between 0.6 and 1 nm. Since the absorption and phaseproperties of materials greatly depend upon the X-ray wavelength used, amaterial must be so selected as to meet the wavelength used in exposure.However, synchrotron radiation has a continuous spectrum with a widewavelength region, so a suitable absorber and mask material vary fromone spectral characteristic to another. No prior art considers thispoint.

For example, Jpn. Pat. Appln. KOKAI Publication No. 5-13309 has proposeda technique which performs exposure to X-rays having a wavelength of 1to 1.5 nm by using Co, Ni, Cu, Zn, and their alloys as absorbermaterials. However, this reference describes only the absorption of Co,Ni, Cu, and Zn at one specific wavelength of 1.225 nm, as the wavelengthof the above wavelength region, and the absorber film thickness at amask contrast of 10. That is, this reference does not take account ofabsorption characteristics, phase shift characteristics, and maskcontrast obtained when exposure is performed by synchrotron radiationwith a wide wavelength region of 0.6 to 1 nm, and optimization of theexposure wavelength when X-ray exposure and pattern-transfer is actuallyperformed by using these absorber materials. According to the techniqueof this reference, the wavelengths of the absorption edges of therespective elements exist within the X-ray wavelength region of 1 to 1.5nm. So, these elements are unsuited to improving the absorptioncharacteristics and phase shift characteristics.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide anX-ray mask which, in proximity X-ray lithography using synchrotronradiation having a maximum light intensity of light entering a mask unitat a wavelength of 0.6 to 1 nm, can decrease the film thickness of anabsorber by the use of a material having large absorption in thisexposure wavelength region and thereby can contribute to, e.g.,improvements of the exposure accuracy in the X-ray exposure, a method ofmanufacturing the same, and an X-ray exposure method.

It is another object of the present invention to provide an X-ray maskwhich, in X-ray exposure using synchrotron radiation having a maximumlight intensity of light entering a mask unit at a wavelength of 0.6 to1 nm, can improve the resolution of transfer patterns by the use of amaterial having a controlled phase shift amount and thereby cancontribute to, e.g., improvements of the exposure accuracy in the X-rayexposure, a method of manufacturing the same, and an X-ray exposuremethod.

According to one aspect of the present invention, there is provided anX-ray exposure method comprising supporting an X-ray mask unit in whicha patterned X-ray absorber is formed on a membrane, the patterned X-rayabsorber containing one of an element having a density/atomic weight ofnot less than 0.085 [g/cm³] and an L-shell absorption edge at awavelength of 0.75 to 1.6 nm and an element having a density/atomicweight of not less than 0.04 [g/cm³] and an M-shell absorption edge at awavelength of 0.75 to 1.6 nm; and applying synchrotron radiation havingmaximum light intensity at a wavelength of 0.6 to 1 nm onto the X-raymask unit.

According to another aspect of the present invention, there is providedan X-ray exposure method comprising supporting an X-ray mask unit inwhich a patterned X-ray absorber is formed on a membrane, the patternedX-ray absorber being formed of one of an alloy and a multi-layer film,which comprises a first material containing an element having an L-shellabsorption edge or an M-shell absorption edge at a wavelength of 0.75 to1.6 nm and a second material containing an element having an M-shellabsorption edge at a wavelength of 0.5 to 0.75 nm; and applyingsynchrotron radiation having maximum light intensity at a wavelength of0.6 to 1 nm onto the X-ray mask unit.

According to still another aspect of the present invention, there isprovided an X-ray exposure method comprising supporting an X-ray maskunit in which a patterned X-ray absorber is formed on a membrane, thepatterned X-ray absorber being a material containing as a majorconstituent an element having all L- and M-shell absorption edges in aregion shorter than the shortest wavelength or longer than the longestwavelength of an exposure wavelength region having an intensity not lessthan {fraction (1/10)} the light intensity at a wavelength of maximumlight intensity of synchrotron radiation to be incident; and applyingthe synchrotron radiation onto the X-ray mask unit.

According to another aspect of the present invention, there is providedan X-ray mask comprising a membrane; and a patterned X-ray absorberformed on the membrane, wherein the patterned X-ray absorber is formedof one of an alloy and a multi-layer film, which comprises a firstmaterial having all L- and M-shell absorption edges in a region shorterthan the shortest wavelength or longer than the longest wavelength of anexposure wavelength region having an intensity not less than {fraction(1/10)} the light intensity at a wavelength of maximum light intensityof synchrotron radiation to be incident and having one absorption edgein a wavelength region from the shortest wavelength of the exposurewavelength region to a wavelength shorter by 0.4 nm than the shortestwavelength, and a second material having all L- and M-shell absorptionedges in a region shorter than the shortest wavelength or longer thanthe longest wavelength of the exposure wavelength region and having oneabsorption edge in a wavelength region from the longest wavelength ofthe exposure wavelength region to a wavelength longer by 0.6 nm than thelongest wavelength.

According to still another aspect of the present invention, there isprovided a method of manufacturing an X-ray mask, comprising supportinga mask substrate including a first X-ray transparent layer, a secondX-ray transparent layer as a patterning layer formed on the first X-raytransparent layer; forming an X-ray absorber film in a concave portionof the second X-ray transparent layer; and polishing an unnecessaryportion of the X-ray absorber film while applying a pressure by fluidfrom a side of the mask substrate opposite to the first X-raytransparent layer.

Additional objects and advantages of the invention will be set forth inthe description which follows, and in part will be obvious from thedescription, or may be learned by practice of the invention. The objectsand advantages of the invention may be realized and obtained by means ofthe instrumentalities and combinations particularly pointed outhereinafter.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate presently preferred embodiments ofthe invention, and together with the general description given above andthe detailed description of the preferred embodiments given below, serveto explain the principles of the invention in which:

FIG. 1 is a sectional view showing the structure of an X-ray mask of thepresent invention;

FIG. 2 is a graph showing the intensity distribution of synchrotronradiation;

FIG. 3 is a graph showing the absorption spectra of Cu, Gd, Ta, W, andAu;

FIGS. 4A and 4B are graphs showing the absorption spectra and maskcontrast of Gd_(x)Au_(y);

FIG. 5 is a graph showing the phase shift spectra of Ni, Cu, Ta, W, Au,and Cu-SiO₂;

FIG. 6 is a graph showing the phase shift spectra of Group I (Co, Ni,Cu, Zn, and Ga);

FIG. 7 is a graph showing the phase shift spectra of Group II (Tc, Rh,Pd, Ag, and Te);

FIG. 8 is a graph showing the phase shift spectra of Group III (La, Ce,Nd, Sm, and Eu);

FIG. 9 is a graph showing the phase shift spectra of Group IV (Ir, Pt,Au, Pb, and Fr);

FIG. 10 is the phase shift spectra of Co, Ni, Cu, and Zn;

FIGS. 11A and 11B are graphs showing the phase shift spectra and maskcontrast of Sm_(x)Au_(y);

FIGS. 12A to 12C are sectional views showing the structure of the X-raymask of the present invention (D_(a)=D_(t));

FIGS. 13A and 13B are sectional views showing the structure of the X-raymask of the present invention (D_(a)<D_(t));

FIGS. 14A and 14B are sectional views showing the structure of the X-raymask of the present invention (D_(a)>D_(t));

FIG. 15 is a graph showing the transmission spectra of Si₃N₄, SiC, Si,and diamond films;

FIG. 16 is a graph showing the transmission spectra of Mg, Al, Si, MgO,Al₂O₃, and SiO₂ films;

FIG. 17 is a graph showing the transmission spectra of Ca, Sc, Ti, CaO,Sc₂O₃, and TiO₂ films;

FIG. 18 is a graph showing the transmission spectra of Sr, SrO, and SrF₂films;

FIG. 19 is a graph showing the transmission spectra of Y, Zr, Y₂O₃, andZrO₂ films;

FIG. 20 is a graph showing the phase shift spectra of the X-ray maskwith an Au absorber buried in various transparent patterned-films;

FIG. 21 is a graph showing the phase shift spectra of the X-ray maskwith an Cu absorber buried in various transparent patterned-films;

FIG. 22 is a graph showing the phase shift spectra of the X-ray maskwith an Ni absorber buried in various transparent patterned-films;

FIG. 23 is a view showing the arrangement of an X-ray exposure apparatusaccording to the 11th embodiment;

FIGS. 24A to 24D are sectional views showing the steps of manufacturingan X-ray mask according to the 12th embodiment;

FIGS. 25A to 25D are sectional views showing the steps of manufacturingthe X-ray mask according to the 12th embodiment;

FIGS. 26A to 26C are sectional views for explaining the effect of the12th embodiment; and

FIG. 27 is a sectional view for explaining a polishing apparatusaccording to the 13th embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings, wherein like reference numerals designateidentical or corresponding parts throughout the several views, and moreparticularly to FIGS. 1-27 thereof, there are illustrated variousexemplary embodiments of the present invention as will now be describedin detail.

(First Embodiment)

As shown in FIG. 1, an X-ray mask 1 is manufactured by forming X-rayabsorber patterns 5 on a membrane 6 as a thin X-ray transparent film andsupporting the periphery of this membrane 6 by a support 7. The basicstructure as a mask is similar to those of conventional masks. However,as will be described later, this embodiment greatly differs from theconventional masks in constituent material, particularly absorbermaterial.

Synchrotron radiation is used as X-rays 4. This synchrotron radiationhas a storage ring with electron energy of 600 MeV, a deflectingmagnetic field of 3T, a maximum storage current of 500 mA, a maximumexposure area of 30 mm square, a maximum exposure intensity of 50mW/cm², and a beam divergence of 2 rad or less. As X-ray extractingwindows, a beryllium (Be) window having an average film thickness of 25μm, a silicon nitride (Si₃N₄) window having an average film thickness of1.5 μm, and a diamond window having an average film thickness of 1.0 μmare used. Also, oblique incident type platinum (Pt) mirrors are used ascondenser and rocking mirrors. As this synchrotron radiation, radiationhaving a wavelength region of 0.62 to 1.02 nm is obtained. FIG. 2 showsthe radiation intensity spectra after transmission through 1.0-μm thickmembrane materials, i.e., a silicon nitride (Si₃N₄) film, siliconcarbide (SiC) film, diamond film, and silicon (Si) film. As shown inFIG. 2, the synchrotron radiation is an exposure light source suited toimproving the pattern accuracy of an object to be exposed. As a resistmaterial, a novolak resin-based chemically amplified type negativeresist (film thickness d_(R)=0.3 μm) is used.

Table 1 below shows the mask contrasts of various materials obtainedwhen an X-ray mask having the structure shown in FIG. 1 is used underthe aforementioned exposure conditions by using one of a 1- or 2-μmthick silicon nitride (Si₃N₄) film, silicon carbide (SiC) film, diamondfilm, and silicon (Si) film as the membrane 6 and setting a filmthickness d_(a) of the absorber 5 to 0.4 μm.

TABLE 1 Dia- Dia- Atomic Density Si₃N₄ SiC mond Si Si₃N₄ SiC mond Sinumber [g/cm³] Absorption edge wavelength λ[Å] 1 μm 1 μm 1 μm 1 μm 2 μm2 μm 2 μm 2 μm Gd 64 7.90 L1:1.478,L2:1.563,L3:1.711,M4:10.0-11.0, 5.405.45 5.25 **5.48 5.38 5.46 5.13 **5.53 M5:10.0-11.0 Tb 65 8.23L1:1.422,L2:1.502,L3:1.650,M5:10.000 5.01 5.03 4.89 **5.04 5.04 5.074.84 **5.10 Sm 62 7.52 L1:1.600,L2:1.695,L3:1.846,M4:11.288, 4.87 4.914.73 **4.94 4.87 4.93 4.63 **4.99 M5:11.552 Ho 67 8.80L1:1.319,L2:1.391,L3:1.537,M5:9.180 **4.91 4.87 4.86 4.85 **5.05 4.994.95 4.93 Ir 77 22.42 M1:3.915,M2:4.260,M3:4.861,M4:5.830, 4.82 4.874.71 **4.90 4.78 4.85 4.59 **4.92 M5:6.050 *Pt 78 21.45M1:3.762,M2:4.093,M3:4.686,M4:5.590, 4.79 4.84 4.63 **4.88 5.05 5.074.88 **5.09 M5:5.810 Dy 66 8.55 L1:1.369,L2:1.444,L3:1.592,M3:7.414,4.83 **4.82 4.75 4.82 4.91 **4.90 4.76 4.88 M5:9.570 Os 76 22.57M1:4.071,M2:4.433,M3:5.043,M4:6.073, 4.60 4.63 4.59 **4.66 4.51 4.564.50 **4.61 M5:6.300 *Au 79 19.32 M1:3.616,M2:3.936,M3:4.518,M4:5.374,4.42 4.47 4.29 **4.50 4.40 4.47 4.18 **4.54 M5:5.584 Tm 69 9.32L2:1.289,L3:1.433,M5:8.487 4.34 4.29 **4.35 4.25 4.50 4.40 **4.50 4.32Re 75 21.02 M1:4.236,M2:4.620,M3:5.234,M4:6.330, 4.14 4.15 **4.23 4.174.00 4.04 **4.18 4.07 M5:6.560 Er 68 9.07L1:1.271,L2:1.339,L3:1.484,M4:8.601, **4.19 4.15 4.19 4.12 **4.32 4.254.30 4.19 M5:8.847 Pm 61 7.22 L1:1.667,L2:1.768,L3:1.919,M4:12.070 4.024.05 3.91 **4.08 4.02 4.07 3.83 **4.11 *W 74 19.30M1:4.407,M2:4.815,M3:5.435,M4:6.590, 3.88 3.89 **4.04 3.89 3.76 3.77**4.03 3.78 M5:6.830 Cu 29 8.93 K:1.381,L2:13.014,L3:13.288,M1:110.600,3.89 3.93 3.77 **3.97 3.87 3.94 3.66 **4.00 M2:159.500,M3:166.000 Nd 607.00 L1:1.739,L2:1.844,L3:1.997,M4:12.459, 3.69 3.72 3.60 **3.74 3.693.73 3.54 **3.77 M5:12.737 Ni 28 8.85K:1.488,L2:14.242,L3:14.525,M3:188.400 3.54 3.57 3.43 **3.60 3.52 3.583.34 **3.63 *Ta 73 16.65 L3:1.255,M1:4.585,M2:5.020,M3:5.650, 3.45 3.44**3.58 3.43 3.37 3.36 **3.61 3.36 M4:6.870,M5:7.110 *Conventionalabsorber material **Maximum mask contrast value

As is apparent from Table 1, Gd, Tb, Sm, Ho, Ir, Pt, Dy, and Os areelements which have larger absorption than conventional materials Au, W,and Ta and hence are suitable absorber materials in X-ray exposure usingsynchrotron radiation having a wavelength region of 0.6 to 1 nm.Additionally, higher mask contrasts than when Ta is used can be obtainedwhen Tm, Er, Pm, Cu, Nd, and Ni are used, so these elements are suitableabsorber materials.

Also, this embodiment reveals that elements as absorber materials bywhich large absorption and high contrast can be obtained in X-rayexposure using synchrotron radiation having a wavelength region of 0.6to 1 nm are classified into the following three groups in accordancewith the relationship between the number density of atoms and theposition of an absorption edge wavelength:

1) Atomic numbers 27 to 31: Co(27) to Ga(31)

2) Atomic numbers 57 to 71: La(57) to Lu(71)

3) Atomic numbers 72 to 80: Hf(72) to Hg(80)

The reasons why large absorption and high mask contrast are obtainedwhen elements in these groups are used in X-ray exposure usingsynchrotron radiation having a wavelength region of 0.6 to 1 nm will bedescribed below.

The complex refractive index and absorption and extinction coefficientsof a material in a soft X-ray region are represented by equations (1) to(4) below. As indicated by equation (4), the absorption coefficient ofthe elements is proportional to the number density of atoms N_(a) timesthe imaginary part of the atomic scattering factors f₂. So, the maskcontrast also depends upon the number density of atoms N_(a) times theimaginary part of the atomic scattering factors f₂. $\begin{matrix}\begin{matrix}{{n - {ik}} = {1 - \delta - {i\quad \beta}}} \\{= {1 - {\left( {N_{a}r_{e}{\lambda^{2}/2}\pi} \right)\left( {f_{1} + {if}_{2}} \right)}}}\end{matrix} & (1) \\{\delta = {N_{a}r_{e}\lambda^{2}{f_{1}/2}\pi}} & (2) \\{k = {\beta = {N_{a}r_{e}\lambda^{2}{f_{2}/2}\pi}}} & (3) \\{\alpha = {{4{{\pi k}/\lambda}} = {2N_{a}r_{e}{\lambda f}_{2}}}} & (4)\end{matrix}$

where

N_(a): number density of atoms

r_(e): classical electron radius (2.81794×10⁻¹⁵[m])

λ: X-ray wavelength

f₁, f₂: real and imaginary parts of atomic scattering factor

n: refractive index

α: (linear) absorption coefficient [cm⁻¹]

k: extinction coefficient

The number density of atoms N_(a) is proportional to density/atomicweight (D/M). High-number density elements having a D/M of 0.085 [g/cm³]or more are those belonging to the following groups:

A) Atomic numbers 22 to 31 (Ti-Ga) (4.54-8.93 g/cm³) D/M=0.085-0.151

B) Atomic numbers 41 to 47 (Nb-Ag) (8.56-12.44 g/cm³) D/M=0.092-0.1

C) Atomic numbers 73 to 79 (Ta-Au) (16.65-22.57 g/cm³) D/M=0.092-0.119

The imaginary part of the atomic scattering factors f₂ changes inaccordance with the wavelength and particularly shows a large changenear the absorption edge. The imaginary part of the atomic scatteringfactors f₂ is large near shorter wavelengths than the absorption edgewavelength and extremely small near longer wavelengths than theabsorption edge wavelength. When a synchrotron radiation source is used,therefore, absorption covers the entire wavelength region of theradiation, so the absorption and mask contrast greatly depend upon theposition of the absorption edge wavelength of an element. In X-rayexposure using synchrotron radiation having a wavelength region of 0.6to 1 nm under the aforementioned exposure conditions (exposure light,window materials, and membrane materials), the following elements whoseabsorption edge wavelengths exist at a wavelength of 0.75 to 1.6 nm nearthe long-wavelength side of the wavelength region of the radiationincrease the imaginary part of the atomic scattering factors f₂:

D) Atomic numbers 27 to 35 (Co-Br) L-shell absorption edge 0.75 to 1.6Tum

E) Atomic numbers 56 to 71 (Ba-Lu) M-shell absorption edge 0.75 to 1.6nm

Elements belonging to groups A) to D), i.e., elements having adensity/atomic weight of 0.085 [g/cm³] or more and the L-shellabsorption edge at a wavelength of 0.75 to 1.6 nm are Co, Ni, Cu, Zn,and Ga having atomic numbers 27 to 30. In these elements, since theL-shell absorption edge is λ=1 to 1.6 nm, i.e., near the long-wavelengthside of the wavelength region of synchrotron radiation (0.6 to 1 nm),the imaginary part of the atomic scattering factors f₂ is large and thenumber density of atoms N_(a) is high. Consequently, the absorptionindex increases, and the mask contrast becomes 2.5 or more for anabsorber film thickness of 0.4 μm. Therefore, Co, Ni, Cu, and Zn arebest absorber materials in X-ray exposure using synchrotron radiationhaving a wavelength region of 0.6 to 1 nm.

Analogously, all elements but Ba in group B) in which the M-shellabsorption edge is λ=0.7 to 1.5 nm, i.e., lanthanoid elements La, Ce,Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu having atomic numbers57 to 71 have M-shell absorption edges near the long-wavelength side ofthe wavelength region of synchrotron radiation, so the imaginary part ofthe atomic scattering factors f2 increases. This increases theabsorption coefficient of the elements although each element has a lownumber density of atoms. Consequently, the mask contrast of an elementhaving a density/atomic weight of 0.040 [g/cm³] or more is 2.5 or morefor an absorber film thickness of 0.4 μm. Ba has an extremely lowdensity/atomic weight of 0.025 [g/cm³] and a low number density of atomsN_(a), so neither the absorption coefficient nor the mask contrastincreases.

Accordingly, La to Lu having atomic numbers 57 to 71 in group E) arealso suitable absorber materials in X-ray exposure using synchrotronradiation having a wavelength region of 0.6 to 1 nm. In particular, Gd,Tb, Sm, and Ho have larger absorption than Ir, Pt, Au, W, and Ta in awavelength region of 0.6 to 1 nm; the largest absorption and maskcontrast can be obtained by these elements among other elements (excepturanium). Therefore, Gd, Tb, Sm, and Ho are good absorber materials.

In contrast, although elements Nb to Ag having atomic numbers 41 to 47in group B) have high number densities of atoms N_(a), their L-shellabsorption edges are λ=2.5 to 0.5 nm, i.e., the wavelength region of theradiation exists on the long-wavelength side of the absorption edge.Hence, with these elements, the imaginary part of the atomic scatteringfactors f₂ decreases, and the mask contrast does not increase very much.

Also, high-density materials Ta, W, and Au (16.65, 19.30, and 19.32g/cm³) having atomic numbers 73 to 79 in group C) and conventionallyused as absorber materials have M4 and M5 absorption edges at awavelength of 0.4 to 0.7 nm. If the wavelength is longer than theabsorption edge, absorption abruptly reduces. Therefore, absorption isextremely small at longer wavelengths than the M4 and M5 absorption edgewavelengths. In particular, Ta and W have absorption edges near a Kabsorption edge of 0.6738 nm of Si. When Si-based materials are used asthe membrane material and the window material, therefore, thisabsorption overlapping allows the membrane to absorb (attenuate) lighthaving a wavelength of 0.6738 nm or less, so Ta and W do not helpincrease the mask contrast. Consequently, the values of absorption andmask contrast of Ta and W are lower than those of Ir, Pt, and Au in thesame group.

From the foregoing, elements by which high mask contrast can be obtainedin X-ray exposure using synchrotron radiation having a wavelength regionof 0.6 to 1 nm can be classified into the following three groups inaccordance with the relationship between the number density of atoms andthe absorption edge wavelength:

1) Atomic numbers 27 to 31 Co(27) to Ga(31)

2) Atomic numbers 57 to 71 La(57) to Lu(71)

3) Atomic numbers 72 to 80 Hf(72) to Hg(80)

FIG. 3 shows the absorption spectra of elements Cu, Gd, Ta, W, and Aubelonging to these groups 1) to 3). Although Cu has a lower density thanthat of Ta or W, its number density of atoms Na is high, and the beamwavelength region exists near the short-wavelength side of the Labsorption edge. Therefore, the imaginary part of the atomic scatteringfactors f₂ is large, and the absorption is larger than those by Ta and Wat a wavelength of 0.7 nm or more. This produces high mask contrast. Theimaginary part of the atomic scattering factors f₂ of Gd is also largebecause the beam wavelength region exists near the short-wavelength sideof its M absorption edge. This obviously increases the absorptioncoefficient and mask contrast.

Table 2 below shows film thicknesses required to obtain a mask contrastof 10 by using the principal elements described above.

TABLE 2 Si₃N₄ SiC Diamond Si membrane membrane membrane membrane Co883.6 877.0 910.4 871.4 Ni 761.2 755.3 784.2 750.4 Cu 704.5 699.0 725.4694.8 Zn 798.7 792.7 822.3 787.7 Sm 588.8 585.9 601.7 583.3 Gd 552.2549.3 562.4 547.0 Tb 583.1 582.2 592.4 581.5 Ir 598.0 594.5 609.1 591.6*Au 634.7 630.5 650.3 627.0 *Pt 601.0 597.0 615.8 593.9 *Ta 808.5 808.6790.3 808.8 *W 713.5 712.5 697.7 711.6

As shown in Table 2, each of Cu, Sm, Gd, and Tb has larger X-rayabsorption than those by Ta and W, so the film thickness can bedecreased. In particular, Sm, Gd, and Tb have larger absorption thanthat by Au and allow thinner film formation. Other elements Ho and Tmalso have larger absorption than that by Au.

In the transfer of fine patterns having a line width of 0.2 μm or less,the film thickness of an absorber by which X-ray beams are wellattenuated increases the ratio (aspect ratio) to the pattern line width.Therefore, it is difficult to accurately form an absorber pattern byusing the conventionally proposed absorber materials and maskfabrication methods. However, an absorber selected by this embodimenthas large absorption of X-ray beams used in exposure and hence allowsthin film formation and easy micropatterning.

(Second Embodiment)

The absorption characteristics of an absorber material can be furtherimproved by combining elements used singly in the first embodiment. Thatis, an alloy or multi-layer film which is formed, as an absorber, bycombining one of elements of atomic numbers 27 to 31 (Co to Ga) ingroup 1) having L-shell absorption edges at longer wavelengths (0.75 to1.6 nm) than an exposure wavelength region of 0.6 to 1 nm and one ofelements of atomic numbers 72 to 80 (Hf to Hg) in group 3) havingM-shell absorption edges at shorter wavelengths (0.5 to 0.75 nm) thanthe exposure wavelength region has large absorption for the synchrotronradiation with a wavelength region of 0.6 to 1 nm. Since high maskcontrast can be obtained without increasing the film thickness of anabsorber, this alloy or multi-layer film is a good absorber material.

Analogously, an alloy or multi-layer film formed by combining one oflanthanoid rare earth elements of atomic numbers 57 to 71 (La to Lu) ingroup 2) having M-shell absorption edges at longer wavelengths (0.75 to1.6 nm) than an exposure wavelength region of 0.6 to 1 nm and one ofelements of atomic numbers 72 to 80 (Hf to Hg) in group 3) havingM-shell absorption edges at shorter wavelengths (0.5 to 0.75 nm) thanthe exposure wavelength region has large absorption for the synchrotronradiation with a wavelength region of 0.6 to 1 nm. High contrast can beobtained by this material without increasing the film thickness of anabsorber, so the material is a good absorber material.

In particular, the combination of one of elements Sm, Gd, Tb, Dy, and Hoin group 2) and one of elements Ir, Pt, and Au in group 3) is also asuitable material as a constituent element of a compound because themask contrasts of the original elements are high. For example, in thecombination of Au and Sm, Sm has larger absorption than Au (maskcontrasts for a film thickness of 0.4 μm are Sm: 4.73 to 4.94 and Au:4.29 to 4.50) and changes its absorption characteristic. Therefore, veryhigh mask contrast can be obtained (Sm₃Au₂: 5.78 to 6.10). Table 3 belowshows the results of calculations of the mask contrasts of alloys andcompounds when the density of a binary compound is calculated by theintegration from the densities of elements in accordance with thecomposition ratio, the absorber film thickness is 0.4 μm, and themembrane thickness is 1 μm.

TABLE 3 Si₃N₄ SiC Diamond Si membrane membrane membrane membrane Alloysof Ir and lanthanoid rare-earth elements Sm₁₁Ir₉ 7.00 7.06 6.76 7.12Gd₁₁Ir₉ 7.67 7.75 7.42 7.82 Tblr 7.05 7.10 6.85 7.15 Dylr 6.88 6.91 6.726.94 Holr 7.11 7.11 6.97 7.12 Tm₂Ir₃ 6.57 6.57 6.48 6.56 Alloys of Ptand lanthanoide rare-earth elements Sm₁₁Pt₉ 6.65 6.71 6.40 6.77 Gd₁₁Pt₉7.26 7.34 7.00 7.40 Tb₁₁Pt₉ 6.72 6.77 6.50 6.81 DyPt 6.57 6.60 6.38 6.63HoPt 6.80 6.81 6.63 6.82 Tin₂Pt₃ 6.33 6.33 6.20 6.33 Alloys of Au andlanthanoide rare-earth elements Sm₃Au₂ 5.99 6.05 5.78 6.10 Gd₃Au₂ 6.546.61 6.32 6.66 Tb₃Au₂ 6.07 6.11 5.89 6.15 Dy₁₁Au₉ 5.94 5.97 5.79 5.99Ho₁₁Au₉ 6.14 6.15 6.01 6.15 Tm₂Au₃ 5.72 5.73 5.61 5.73

The values of mask contrasts of the alloys and compounds in Table 3 arehigher than the value of any element, i.e., mask contrasts much higherthan those of the elements can be obtained. FIGS. 4A and 4B show changesin the absorption characteristic and mask contrast when the compositionof Gd_(1-X)Au_(X) was changed. As shown in FIGS. 4A and 4B, the maskcontrast improves in accordance with the absorption characteristicchange.

In addition to compounds of the combinations shown in Table 3, binarycompounds of Ta(73) and

1) elements of atomic numbers 30 to 33: Zn(30) to As(33)

2) elements of atomic numbers 56 to 72: Ba(56) to Hf(72)

3) elements of atomic number 75 and subsequent numbers: Re(75) to Bi(83)

have higher contrasts than that of any of these constituent elements.

Similarly, binary compounds of W(74) and

1) elements of atomic numbers 32 and 33: Ge(32) and As (33)

2) elements of atomic numbers 56 to 72: Ba(56) to Hf (72)

3) elements of atomic numbers 75 to 79: Re(75) to Au(79)

have higher mask contrasts than that of any of these constituentelements.

Also, high mask contrasts can be obtained by binary compounds of Re(75)or Os(76) and

elements of atomic numbers 56 to 79: Ba(56) to Au(79),

binary compounds of Ir(77) and

elements of atomic numbers 56 to 78: Ba(56) to Pt(78), and

binary compounds of Pt(78) or Au(79) and elements of atomic numbers 56to 77: Ba(56) to Ir(77).

Consequently, these alloys and compounds are effective materials fordecreasing the absorber film thickness and hence are good absorbermaterials.

Table 4 below shows film thicknesses necessary to obtain a mask contrastof 10 in absorbers composed of the above principal alloys and compounds.

TABLE 4 Si₃N₄ SiC Diamond Si membrane membrane membrane membrane Alloysof Ir and lanthanoid rare-earth elements Sm₁₁Ir₉ 476.5 474.0 485.7 472.0Gd₁₁Ir₉ 454.2 452.0 462.1 450.0 TbIr 474.5 472.8 482.1 471.1 DyIr 480.8479.6 487.2 478.8 HoIr 473.0 473.0 478.1 472.8 Alloys of Pt andlanthanoide rare-earth elements Gd₁₁Pt₉ 467.5 465.0 477.0 462.9 Tb₁₁Pt₉487.2 485.4 496.6 483.6 HoPt 484.5 484.1 491.1 483.7 Alloys of Au andlanthanoide rare-earth elements Sm₃Au₂ 519.7 516.7 531.3 514.5 Gd₃Au₂494.3 491.7 504.3 489.5 Tb₃Au₂ 515.6 513.7 525.4 511.9 Ho₁₁Au₉ 513.3513.1 519.9 513.1 Conventional absorber material Au 634.7 630.5 650.3627.0 Pt 601.0 597.0 615.8 593.9 Ta 808.5 808.6 790.3 808.8 W 713.5712.5 697.7 711.6

As is evident from Table 4, each of these alloys and compounds haslarger absorption than any single element, so the film thickness can bedecreased. That is, the required film thickness to obtain a maskcontrast of 10 can be greatly decreased to 500 nm or less when, e.g.,compounds Gd₁₁Ir₉, Gd₃Au₂, and Gd₁₁Pt₉ having mask contrasts of 6.50 ormore in Table 3 are used. Accordingly, when any of the alloys andcompounds proposed in this embodiment is used as an absorber, exposurelight having a wavelength region of 0.6 to 1 nm is largely absorbed, sothe film thickness of the absorber material can be decreased. Thisallows easy micropatterning in the manufacture of masks.

(Third Embodiment)

A phase shift mask suitable for the proximity X-ray lithography usingsynchrotron radiation will be proposed. This phase shift mask is made ofan absorber material by which a difference |Φ₁-Φ₂| between shift amountsof phases Φ₁ and Φ₂ of X-rays transmitted through an absorber and a masksubstrate is constant over the wavelength band of exposure light havingan exposure wavelength region of 0.6 to 1 nm in which high resolution isobtained, and by which high mask contrast can be obtained at the sametime. Also, an X-ray exposure method using the mask will be explained.

First, a good absorber material by which the difference |Φ₁-Φ₂| betweenshift amounts of the phases Φ₁ and Φ₂ of X-rays transmitted through anabsorber and a mask substrate does not largely change with thewavelength in exposure by the synchrotron radiation having an exposurewavelength region of 0.6 to 1 nm will be described below.

A desirable wavelength region of synchrotron radiation is 0.6 to 1 nm.The wavelength region of synchrotron radiation used in this embodimentis 0.62 to 1.02 nm, so this synchrotron radiation is a desirableexposure light source. However, in exposure using this synchrotronradiation as a light source, a Be window (average film thickness 25 μm),Si₃N₄ window (average film thickness 1.5 μm), and diamond window(average film thickness 1.0 μm) are used as extracting windows. Thewavelength region from the maximum intensity to the {fraction (1/10)}intensity in an intensity spectrum after transmission through thesematerials is 0.654 to 1.015 nm. Si has its absorption edge at awavelength of 0.674 nm. Therefore, under normal exposure conditionsusing an Si-based material as the window material or membrane material,exposure light having a wavelength of 0.674 nm or less attenuatesstrongly by Si absorption. Since this wavelength region of X-ray beamsdoes not have large influence on exposure, the wavelength regioncontributing to exposure is 0.654 to 1.015 nm. So, a suitable absorbermaterial in this effective wavelength region is desirable.

Table 5 below shows the dispersions of phase shift angles of variouselements, as ΔΦ, when a film thickness d_(a) is so set that the averageof phase shift angles of an absorber in the wavelength region of 0.654to 1.015 run was π (ΔΦ: the deviation of a phase shift amount from π).

TABLE 5 Deviation of Atomic phase shift angle π phase shift film Si₃N₄SiC Diamond Si number Δφ[π] thickness d_(a) [nm] Absorption edgewavelength λ[Å] 1 μm 1 μm 1 μm 1 μm Co 27 ±0.18 586.3K:1.608,L2:15.618,L3:15.915,M23:202.00 4.82 4.88 4.64 4.93 Ni 28 ±0.16566.5 K:1.488,L2:14.242,L3:14.525,M3:188.40 5.77 5.84 5.52 5.91 Cu 29*±0.13 612.4 K:1.381,L2:13.014,L3:13.288,M1:110.60,M2:159.50,M3:166.007.57 7.68 7.19 7.77 Zu 30 *±0.10 790.2K:1.283,L1:10.348,L2:11.862,L3:12.31,M2:137.00,M3:143.90 9.94 10.10 9.3610.23 Ga 31 *±0.07 1039.8 L1:9.517,L2:10.828,L3:11.100,M23:119.70 13.3813.61 12.49 13.81 Pd 46 ±0.21 487.5 L1:3.427,L2:3.723,L3:3.907,M5:37.0003.83 3.87 3.72 3.90 Ag 47 ±0.21 556.0L1:3.256,L2:3.516,L3:3.700,M4:31.140,M5:30.820 4.07 4.12 3.94 4.15 La 57*±0.08 1181.8 L1:1.978,L2:2.105,L3:2.261,M5:14.900 18.13 18.44 16.9018.71 Ce 58 *±0.11 985.9 L1:1.893,L2:2.012,L3:2.166,M5:14.000 18.6518.99 17.33 19.28 Pr 59 *±0.07 1115.7L1:1.814,L2:1.925,L3:2.079,M4:13.122,M5:13.394 23.29 23.68 21.54 24.03Nd 60 *±0.03 1100.4 L1;1.739,L2:1.844,L3:1.997,M4:12.459,M5:12.737 31.6032.16 29.01 32.65 Pm 61 *±0.05 1072.2L1:1.667,L2:1.768,L3:1.919,M4:12.070 35.38 36.05 32.37 36.63 Sm 62*±0.10 1127.2 L1:1.600,L2:1.695,L3:1.846,M4:11.288,M5:11.552 70.75 72.2463.65 73.54 Ta 73 ±0.54 679.5L3:1.255,M1:4.585,M2:5.020,M3:5.650,M4:6.870,M5:7.110 7.22 7.21 7.557.20 W 74 ±0.56 581.7 M1:4.407,M2:4.815,M3:5.435,M4:6.590,M5:6.830 6.776.78 7.08 6.79 Ir 77 ±0.30 403.7M1:3.915,M2:4.260,M3:4.861,M4:5.830,M5:6.050 4.89 4.93 4.77 4.97 Pt 78±0.27 408.7 M1:3.762,M2:4.093,M3:4.686,M4:5.590,M5:5.810 4.95 5.00 4.785.04 Au 79 ±0.25 441.0 M1:3.616,M2:3.936,M3:4.518,M4:5.374,M5:5.584 5.125.17 4.94 5.21 *| Δφ | ≦ 0.13 π

Table 5 also shows the wavelength at the absorption edge of each elementand the mask contrast obtained for each membrane material when theabsorber film with thickness is so set that the average of phase shiftangles of an absorber in the wavelength region of 0.654 to 1.015 nm wasπ. Table 5 indicates that there is a large difference between the phasecharacteristics of an element having an absorption edges in the beamwavelength region and an element not having absorption edges in thisregion, i.e., the dispersion of the phase shift angle of an element nothaving absorption edges in the beam wavelength region is small.

FIG. 5 and Table 6 below show the phase change characteristics ofprincipal absorbers made from elements having absorption edges in thebeam wavelength region and elements not having absorption edges in thisregion. The phase shifts of the elements Ta and W having such absorptionedges in the wavelength region change abruptly at the absorption edgesM4 and M5 as shown in FIG. 5, so it is difficult to control their phaseshift angles over the whole beam light wavelength region. On the otherhand, the phase shifts of the elements Au, Cu, Ni, Zn, and Cu-SiO₂ (Cuis filled in an SiO₂ film) not having such absorption edges changelittle with the wavelength. So, the phase shift of these elements aresubstantially controllable.

TABLE 6 Ta W Au Absorber film thickness [nm] 679.5 581.70 441.03 Maskcontrast at Si₃N₄ 7.22 (3.45) 6.77 (3.88) 5.12 (4.42) membrane Maskcontrast at SiC 7.21 (3.44) 6.78 (3.89) 5.17 (4.47) membrane Maskcontrast at diamond 7.55 (3.58) 7.08 (4.04) 4.94 (4.29) membrane Maskcontrast at Si membrane 7.20 (3.43) 6.79 (3.89) 5.21 (4.50) Exposurewavelength region 6.54-10.15 6.54-10.15 6.54-10.15 [Å] Deviation Δφ fromthe π ±0.54 ±0.56 ±0.25 phase shift [π] Phase shift controllability 0.47≦ φ ≦ 1.54 0.44 ≦ φ ≦ 1.56 0.75 ≦ φ ≦ 1.25 at above absorber filmthickness in exposure wavelength [π] Cu Ni Zn Cu—SiO₂ Absorber filmthickness [nm] 612.44 566.51 790.25 843.01 Mask contrast at Si₃N₄ 7.57(3.89) 5.77 (3.54) 9.78 (3.34) 12.40 (3.55) membrane Mask contrast atSiC 7.68 (3.93) 5.84 (3.57) 9.93 (3.37) 12.62 (3.58) membrane Maskcontrast at diamond 7.19 (3.77) 5.52 (3.43) 9.21 (3.24) 11.43 (3.42)membrane Mask contrast at Si membrane 7.77 (3.97) 5.91 (3.60) 10.07(3.39) 12.81 (3.61) Exposure wavelength region 6.54-10.15 6.54-10.156.54-10.15 6.54-10.15 [Å] Deviation Δφ from the π ±0.13 ±0.16 ±0.10±0.09 phase shift [π] Phase shift controllability 0.88 ≦ φ ≦ 1.13 0.84 ≦φ ≦ 1.16 0.90 ≦ φ ≦ 1.10 0.91 ≦ φ ≦ 1.09 at above absorber filmthickness in exposure wavelength [π] Numerical values in the parenthesesof mask contrast are obtained for an absorber film thickness of 400 nm

An element not having absorption edges in the wavelength region does notabruptly change its refractive index in the wavelength region.Therefore, the film thickness for X phase shift also changes little withthe wavelength, so phase control of the element is possible. This makesthe element suitable for an absorber material of a phase shift mask.When an X-ray source having a wavelength region of 0.6 to 1 nm is usedin X-ray exposure, elements in the following four groups do not havetheir absorption edges in this wavelength region:

1) Group I atomic numbers 27 to 31: Co(27) to Ga(31)

2) Group II atomic numbers 41 to 52: Nb(41) to Te(52)

3) Group III atomic numbers 57 to 63: La(57) to Eu(63)

4) Group IV atomic numbers 76 to 92: Os(76) to U(92)

So, phase shift control of these elements is readily possible. Since anydesirable phase difference can be controlled by changing the filmthickness, each element is suited for an absorber material of an X-raymask having the phase shift effect. Of these materials, those includedin the materials having large absorption described in the firstembodiment are

Co(27) to Ga(31) of atomic numbers 27 to 31

La(57) to Eu(63) of atomic numbers 57 to 63

Os(76) to Hg(80) of atomic numbers 76 to 80

In X-ray exposure using synchrotron radiation having a wavelength regionof 0.6 to 1 nm, these elements are very suitable absorber materialsexcellent in both the phase characteristic and the absorptioncharacteristic. Elements Fr(87) and Ac(89) to U(92) of atomic numbers 89to 92 also have good phase and absorption characteristics. However,these elements are rare and difficult to obtain, expensive, and henceare impractical, so they are not described in this embodiment.

The aforementioned materials having high phase shift controllability andsuited to an absorber material of a phase shift mask will be describedbelow.

Elements difficult to control over the entire wavelength band of asynchrotron radiation source having a wavelength region of 0.6 to 1 nmare the following elements having absorption edges in the wavelengthregion of 0.654 to 1.015 nm:

1) Atomic numbers 12 to 14: Mg(12) to Si(14)

K-shell absorption edge

2) Atomic numbers 32 to 37: Ge(32) to Rb(37)

L-shell absorption edge

3) Atomic numbers 64 to 75: Gd(64) to Re(75)

M-shell absorption edge

This is because the refractive index abruptly changes at the absorptionedge wavelength, so the film thickness for π phase shift also largelychanges with the wavelength. Ta(73) and W(74) as conventional absorbermaterials in the proximity X-ray lithography are included in theseelements:

Ta (tantalum: atomic number 73)

M-shell absorption edge wavelength: M4: 0.687 nm, M5: 0.711 nm

π phase shift absorber film thickness: d_(a)=679.50 nm (mask contrast:7.20 to 7.55)

π phase shift controllability in the wavelength 0.654 to 1.015 nm:|Φ₁-Φ₂|≦π±0.54 π

w (tungsten: atomic number 74)

M-shell absorption edge wavelength: M4: 0.659 nm, M5: 0.683 nm

π phase shift absorber film thickness: d_(a)=581.70 nm (mask contrast:6.77 to 7.08)

π phase shift controllability in the wavelength 0.654 to 1.015 nm:|Φ₁-Φ₂|≦π±0.56 π

That is, the phase changes by π/2 or more in this wavelength region.Hence, when these materials are used in exposure by a light source usingcharacteristic X-rays with one specific wavelength, the phase shift canbe controlled by the film thickness. However, phase control over thewhole wavelength region is difficult to perform when a synchrotronradiation source is used.

On the other hand, an element not including absorption edges in thewavelength region does not abruptly change its refractive index in thewavelength region. Accordingly, the film thickness for π phase shiftalso changes little with the wavelength, so its phase control ispossible. When an X-ray source having a wavelength region of 0.6 to 1 nmis used in X-ray exposure, elements are classified into four groups,i.e., Co(27) to Ga(31) in Group I, Nb(41) to Te(52) in Group II, La(57)to Eu(63) in Group III, and Os(76) to U(92) in Group IV.

The absorption characteristics and the like of the elements in thesefour groups will be described below.

1) Group I (atomic numbers 27 to 31: Co(27) to Ga(31))

Each element in this group has a density of 5.90 to 8.93 g/cm³ which islower than those of the conventionally used absorber materials. However,the number density of atoms N_(a) is high, and the L-shell absorptionedges exist in λ=1 to 1.6 nm. Since the wavelength region of synchrotronradiation exists near the short-wavelength side of the absorption edges,the imaginary part of the atomic scattering factors f₂ is large, and thevalues of the absorption α and mask contrast are also large. FIG. 6 andTable 7 below show the dispersions of phase shift angles of the elementsin this group for the π phase shift film thickness d_(a) in thewavelength region of 0.654 to 1.015 nm.

TABLE 7 Co Ni Cu Zn Ga Absorber film thickness 586.34 566.51 612.44790.25 1039.80 [nm] Mask contrast at Si₃N₄ 4.82 (2.99) 5.77 (3.54) 7.57(3.89) 9.94 (3.34) 13.38 (2.87) membrane Mask contrast at SiC 4.88(3.02) 5.84 (3.57) 7.68 (3.93) 10.10 (3.37) 13.61 (2.90) membrane Maskcontrast at diamond 4.64 (2.92) 5.52 (3.43) 7.19 (3.77) 9.36 (3.24)12.49 (2.81) membrane Mask contrast at Si 4.93 (3.04) 5.91 (3.60) 7.77(3.97) 10.23 (3.39) 13.81 (2.91) membrane Exposure wavelength region6.54-10.15 6.54-10.15 6.54-10.15 6.54-10.15 6.54-10.15 [Å] Deviation Δφfrom the π ±0.18 ±0.16 ±0.13 ±0.10 ±0.07 phase shift [π] Phase shiftcon- 0.82 ≦ φ ≦ 1.18 0.84 ≦ φ ≦ 1.16 0.88 ≦ φ ≦ 1.13 0.90 ≦ φ ≦ 1.100.93 ≦ φ ≦ 1.07 controllability at above absorber film thickness inexposure wavelength Numerical values in the parentheses of mask contrastare obtained for an absorber film thickness of 400 nm

The deviation of the phase shift angle of each element from π is ΔΦ=0.07to 0.18 π. Therefore, the phase shift angles of the elements in thisgroup can be controlled in exposure in this wavelength region. Inparticular, the phase shift angles of Cu, Zn, and Ga can be controlledto π±0.13 π, π±0.10 π, and π±0.07 π, respectively. That is, the phaseshift can be accurately controlled with respect to any desirable phaseshift amount by changing the film thickness. Since the mask contrastsare also high, the elements in this group are suitable as absorbermaterials in this exposure wavelength region.

2) Group II (atomic numbers 41 to 52: Nb(41) to Te(52))

The L-shell absorption edges of each of elements Nb(41) to Te(52) inthis group exist in λ=0.25 to 0.50 nm. Since the wavelength region ofsynchrotron radiation exists on the long-wavelength side of theabsorption edges, the imaginary part of the atomic scattering factors f₂is small, and the values of the absorption α and mask contrast are alsosmall. FIG. 7 and Table 8 below show the dispersions of the phase shiftangles of the elements in this group for the π phase shift filmthickness d_(a) in the wavelength region of 0.654 to 1.015 nm.

TABLE 8 Tc Ru Rh Pd Ag Te Absorber film 523.42 491.47 474.14 487.46555.96 1012.00 thickness [nm] Mask contrast at 2.91(2.28) 3.17(2.58)3.47(2.88) 3.83(3.04) 4.07(2.79) 6.67(2.19) Si₃N₄ membrane Mask contrastat 2.93(2.29) 3.20(2.60) 3.51(2.90) 3.87(3.06) 4.12(2.81) 6.76(2.20) SiCmembrane Mask contrast at 2.84(2.24) 3.09(2.53) 3.38(2.82) 3.72(2.97)3.94(2.73) 6.38(2.15) diamond membrane Mask contrast at Si 2.95(2.30)3.22(2.61) 3.53(2.92) 3.90(3.08) 4.15(2.83) 6.83(2.21) membrane Exposurewavelength region [Å] 6.54-10.15 6.54-10.15 6.54-10.15 6.54-10.156.54-10.15 6.54-10.15 Deviation Δφ from the π phase shift ±0.22 ±0.22±0.22 ±0.21 ±0.21 ±0.18 [π] Phase shift con- 0.78 ≦ φ ≦ 1.22 0.78 ≦ φ ≦1.22 0.79 ≦ φ ≦ 1.22 0.79 ≦ φ ≦ 1.21 0.80 ≦ φ ≦ 1.21 0.82 ≦ φ ≦ 1.18trollability at above absorber film thickness in exposure wavelength [π]Numerical values in the parentheses of mask contrast are obtained for anabsorber film thickness of 400 nm

The deviation of the phase shift angle of each element from π is ΔΦ=0.18to 0.24 π. That is, the deviations are larger and the mask contrasts arelower than those of the elements in Group I. However, elements Ru(44),Rh(45), and Pd(46) in this group have relatively high densities (12.06to 12.44 g/cm³). So, the film thickness required for π phase shift canbe as very small as 474.14 to 487.46 nm. Since these elements also havelarge absorption, they are good absorber materials.

3) Group III (atomic numbers 57 to 63: La(57) to Eu(63))

All of elements La(57) to Eu(63) are rare-earth elements and have lowdensities of 5.24 to 7.52 g/cm³. As in Group I, however, the absorptionedge (M shell in this case) of each element exist in λ=1.1 to 1.5 nm.Since the wavelength region of synchrotron radiation exists on theshort-wavelength side of this absorption edge, the imaginary part of theatomic scattering factors f₂ is large, and the values of the absorptionα and mask contrast are also large. The larger the atomic number, theshorter the wavelength of the M-shell absorption edge. Consequently, theabsorption edges of Gd to Tm having atomic numbers 64 to 69 overlap thewavelength region of synchrotron radiation. This results in very largeabsorption and mask contrast values.

The film thickness for π phase shift must be as large as 985.88 to1611.3 nm due to the low densities of the elements in Group III.However, the deviation of the phase shift angle of each element from πis |ΔΦ|=0.03 to 0.14 π, i.e., each element has high phase shiftcontrollability. Therefore, any desirable phase shift amount can beaccurately controlled by changing the film thickness. Since elementsLa(57) to Eu(63) also have large absorption, they are suitable absorbermaterials for a phase shift X-ray mask (FIG. 8 and Table 9 below).

TABLE 9 La Ce Pr Nd Pm Sm Eu Absorber film 1181.80 985.88 1115.701100.40 1072.20 1127.20 1611.30 thickness [nm] Mask contrast at18.13(2.81) 18.65(3.49) 23.29(3.24) 31.6(3.69) 35.38(4.02) 70.75(4.87)62.32(3.03) Si₃N₄ membrane Mask contrast at SiC 18.44(2.83) 18.99(3.52)23.68(3.26) 32.16(3.72) 36.05(4.05) 72.24(4.91) 63.67(3.05) membraneMask contrast at 16.90(2.75) 17.33(3.40) 21.54(3.17) 29.01(3.60)32.37(3.91) 63.65(4.73) 56.48(2.97) diamond membrane Mask contrast at Si18.71(2.84) 19.28(3.55) 24.03(3.28) 32.65(3.74) 36.63(4.08) 73.54(4.94)64.86(3.07) membrane Exposure wavelength 6.54-10.15 6.54-10.156.54-10.15 6.54-10.15 6.54-10.15 6.54-10.15 6.54-10.15 region [Å]Deviation Δφ from ±0.08 ±0.11 ±0.08 ±0.03 ±0.05 ±0.10 ±0.14 the π phaseshift [π] Phase shift con- trollability at above absorber film 0.92 ≦ φ≦ 0.89 ≦ φ ≦ 0.93 ≦ φ ≦ 0.97 ≦ φ ≦ 0.95 ≦ φ ≦ 0.90 ≦ φ ≦ 0.86 ≦ φ ≦thickness in 1.08 1.11 1.08 1.03 1.05 1.09 1.14 exposure wavelength [π]Numerical values in the parentheses of mask contrast are obtained for anabsorber film thickness of 400 nm

4) Group IV (atomic numbers 76 to 92: Os(76) to U(92))

Elements Os(76) to Au(79) in this group have very high densities of19.32 to 22.57 g/cm₃, and the values of their absorption α and maskcontrast are also large. However, the M-shell absorption edges of eachelement exist in λ=0.3 to 0.6 nm. Since the maximum light intensitywavelength of synchrotron radiation exists on the long-wavelength sideof this absorption edge, the imaginary part of the atomic scatteringfactors f₂ is smaller than that on the short-wavelength side and itsvicinity of the absorption edge. Therefore, the absorption in thewavelength region has no big difference from Cu in Group I.

The film thickness d_(a) for π phase shift can be decreased to 403.70 to441.03 nm due to the high densities of the elements in Group IV. FIG. 9and Table 10 below show the dispersions of the phase shift angles inthis group for the π phase shift film thickness d_(a) in the wavelengthregion of 0.654 to 1.015 nm.

TABLE 10 Os Ir Pt Au Hg Pb Fr Absorber film 427.30 403.70 408.70 441.03618.16 731.69 828.42 thickness [nm] Mask contrast at 5.08(4.60)4.89(4.82) 4.95(4.79) 5.12(4.40) 5.44(3.05) 6.03(2.73) 9.13(3.01) Si₃N₄membrane Mask contrast at 5.12(4.63) 4.93(4.87) 5.00(4.84) 5.17(4.47)5.50(3.07) 6.10(2.75) 9.25(3.03) SiC membrane Mask contrast at5.06(4.59) 4.77(4.71) 4.78(4.63) 4.94(4.29) 5.25(2.99) 5.80(2.70)8.69(2.95) diamond membrane Mask contrast at Si 5.15(4.66) 4.97(4.90)5.04(4.88) 5.21(4.50) 5.55(3.09) 6.16(2.79) 9.35(3.05) membrane Exposurewavelength 6.54-10.15 6.54-10.15 6.54-10.15 6.54-10.15 6.54-10.156.54-10.15 6.54-10.15 region [Å] Deviation Δφ from ±0.36 ±0.30 ±0.27±0.25 ±0.24 ±0.21 ±0.17 the π phase shift [π] Phase shift con- 0.64 ≦ φ≦ 0.70 ≦ φ ≦ 0.73 ≦ φ ≦ 0.75 ≦ φ ≦ 0.77 ≦ φ ≦ 0.79 ≦ φ ≦ 0.83 ≦ φ ≦trollability at 1.36 1.30 1.27 1.25 1.24 1.21 1.17 above absorber filmthickness in exposure wavelength [π] Numerical values in the parenthesesof mask contrast are obtained for an absorber film thickness of 400 nm

The deviation of the phase shift angles of each element from π isΔΦ=0.12 to 0.36 π. Pt and Au used as an absorber material have ΔΦ=0.27and 0.25 π, respectively. Since the deviations are larger than those ofthe elements in Group I, it is difficult to accurately control a desiredphase shift amount by changing the film thickness (FIG. 9).

Table 11 below collectively shows the results of the elements belongingto Groups I to IV described above.

TABLE 11 Phase shift π phase shift controllability φ[π] Mask Mask MaskMask average film Phase shift deviation contrast contrast contrastcontrast thickness [nm] Δφ[π] Si₃N₄ 1 μm SiC 1 μm C 1 μm Si 1 μm Group ICo(27)-Ga(31) Co 586.34 0.82 ≦ φ ≦ 1.18 4.82 4.88 4.64 4.93 (27) Δφ =±0.18 (2.99) (3.02) (2.92) (3.04) Ni 566.51 0.84 ≦ φ ≦ 1.16 5.77 5.845.52 5.91 (28) Δφ = ±0.16 (3.54) (3.57) (3.43) (3.60) Cu 612.44 0.88 ≦ φ≦ 1.13 7.57 7.68 7.19 7.77 (29) Δφ = ±0.13 (3.89) (3.93) (3.77) (3.97)Zn 790.25 0.90 ≦ φ ≦ 1.10 9.94 10.10 9.36 10.23 (30) Δφ = ±0.10 (3.34)(3.37) (3.24) (3.39) Ga 1039.8 0.93 ≦ φ ≦ 1.07 13.38 13.61 12.49 13.81(31) Δφ = ±0.07 (2.87) (2.90) (2.81) (2.91) Group II Nb(41)-Te(52) Rh474.14 0.79 ≦ φ ≦ 1.22 3.47 3.51 3.38 3.53 (45) Δφ = ±0.22 (2.88) (2.90)(2.82) (2.92) Pd 487.46 0.79 ≦ φ ≦ 1.21 3.83 3.87 3.72 3.90 (46) Δφ =±0.21 (3.04) (3.06) (2.97) (3.08) Ag 555.96 0.80 ≦ φ ≦ 1.21 4.07 4.123.94 4.15 (47) Δφ = ±0.21 (2.79) (2.81) (2.73) (2.83) Group IIILa(57)-Cu(63) La 1181.8 0.92 < φ < 1.08 18.13 18.44 16.90 18.71 (57) Δφ= ±0.08 (2.81) (2.83) (2.75) (2.84) Ce 985.88 0.89 < φ < 1.11 18.6518.99 17.33 19.28 (58) Δφ = ±0.11 (3.49) (3.52) (3.40) (3.55) Pr 1115.70.93 < φ < 1.08 23.29 23.68 21.54 24.03 (59) Δφ = ±0.08 (3.24) (3.26)(3.17) (3.28) Nd 1100.4 0.97 < φ < 1.03 31.60 32.16 29.01 32.65 (60) Δφ= ±0.03 (3.69) (3.72) (3.60) (3.74) Sm 1127.2 0.90 < φ < 1.09 70.7572.24 63.65 73.54 (62) Δφ = ±0.10 (4.87) (4.91) (4.73) (4.94) Eu 1611.30.86 < φ < 1.14 62.32 63.67 56.48 64.86 (63) Δφ = ±0.14 (3.03) (3.05)(2.97) (3.07) Group IV Os(76)-U(92) Ir 403.70 0.70 < φ < 1.30 4.89 4.934.77 4.97 (77) Δφ = ±0.30 (4.82) (4.87) (4.71) (4.90) Pt 408.70 0.73 < φ< 1.27 4.95 5.00 4.78 5.04 (78) Δφ = ±0.27 (4.79) (4.84) (4.63) (4.88)Au 441.03 0.75 < φ < 1.25 5.12 5.17 4.94 5.21 (79) Δφ = ±0.25 (4.40)(4.47) (4.29) (4.50)

Table 11 above shows the absorber film thickness required for π phaseshift, and the phase shift deviation and mask contrast corresponding tothe thickness (numbers in the parentheses indicate the mask contrastvalue for a membrane thickness of 1 μm and an absorber film thickness of0.4 μm).

Of the preferable elements shown in this Table 11, in elements meetingthe following two conditions

1) high phase shift controllability (ΔΦ≦0.20π), and

2) high mask contrast (2.80 or more for an absorber film thickness of0.4 μm)

are

Co, Ni, Cu, and Zn in Group I

Rh, Pd, and Ag in Group II

La, Ce, Pr, Nd, Pm, Sm, and Eu in Group III

At, Rn, Fr, Ac, Th, Pa, and U in Group IV

Accordingly, these elements are absorber materials suited to improvingthe resolution of pattern-transfer by using the phase shift effect.

Furthermore, assume that desirable conditions of phase shift X-ray maskabsorber materials, among other suitable elements described above,having high phase shift controllability, small absorber filmthicknesses, and appropriate mask contrast values are as follows:

1) ΔΦ≦0.125 π (0.92≦|cos|Φ1) the maximum and minimum phase shift amountswith respect to the wavelengths in the exposure wavelength region are±12.5% or less of the average phase shift amount in the exposurewavelength region

2) the mask contrast value is about 10 for the π phase shift filmthickness

3) π phase shift film thickness d_(a)≦1,000 nm (the aspect ratio is 10or less for a line & space pattern width of 0.1 μm)

In X-ray exposure having an exposure wavelength region of 0.65 to 1.02nm, suitable absorber materials meeting all these conditions are

Cu (copper: atomic number 29)

phase shift absorber film thickness: d_(a)=612.40 nm (mask contrast:7.19 to 7.77)

π phase shift controllability: |Φ₁-Φ₂|≦π±0.125 π

Zn (zinc: atomic number 30)

π phase shift absorber film thickness: d_(a)=790.25 nm (mask contrast:9.36 to 10.23)

πphase shift controllability: |Φ₁-Φ₂|≦π±0.10 π

This indicates that Cu and Zn are elements having absorptioncharacteristics and phase characteristics suited to X-ray exposure usingsynchrotron radiation having an exposure wavelength region of 0.6 to 1nm.

Cu and Zn are excellent in absorption and phase

characteristics for synchrotron radiation in the wavelength region of0.6 to 1 nm and exhibit to be suitable as X-ray mask absorber materials.As proposed in Jpn. Pat. Appln. KOKAI Publication No. 5-13309, thesematerials are used for the X-ray beams having a wavelength region of 1to 1.5 nm, the materials have absorption edges within or near thiswavelength region, and the phase shift amounts greatly change withrespect to the wavelengths. It is difficult to control the phase shiftangles. A sufficient phase shift effect cannot be expected (see FIG.10). The phase shift angles of the respective absorbers in thewavelength region of 1 to 1.5 nm, deviations from the average phaseshift amounts, and deviations ratios are shown below:

Co: 0.90π≦Φ≦1.24π, 1.07π±0.20π, ±18.7%

Ni: 0.30π≦Φ≦1.18π, 0.74π±0.44π, ±59.5%

Cu: 0.17π≦Φ≦1.13π, 0.65π±0.48π, ±73.8%

Zn: −0.09π≦Φ≦1.30π, 0.61π±0.70π, ±114.9%

In exposure using synchrotron radiation having the wavelength region of1 to 1.5 nm, therefore, when X-ray masks containing Co, Ni, Cu, and Znas absorbers are used, the absorption amounts for the X-rays in thiswavelength region are large, but phase control is difficult. Theresolution of a transfer pattern in exposure using synchrotron radiationhaving the exposure wavelength of 1 to 1.5 nm is lower than that inexposure using synchrotron radiation having the exposure wavelengthregion of 0.6 to 1 nm.

(Fourth Embodiment)

The phase characteristics of the elements in Group II (atomic numbers 41to 52: Nb to Te) and Group IV (atomic numbers 76 to 92: Os to U), whichhave absorption edges at short wavelengths of 0.2 to 0.6 nm in theexposure light wavelength region of 0.6 to 1 nm, can be improved bycombining them with the elements in Group I (atomic numbers 27 to 31: Coto Ga) and Group III (atomic numbers 57 to 63: La to Eu), which haveabsorption edges at long wavelengths of 1 to 1.6 nm in the exposurelight wavelength region of 0.6 to 1 nm, in the form of alloys orcompounds. Some combinations can greatly improve not only the phasecharacteristic but also the absorption characteristic as described inthe second embodiment.

Improvements of the phase characteristics of alloys and compounds formedby combining the elements in Groups II and IV with the elements inGroups I and III will be described below.

The phase shift angle of an element increases toward longer wavelengthsexcept that it abruptly decreases at the wavelengths of absorptionedges. All elements in Groups I to IV do not have absorption edges inthe exposure wavelength region. So, many materials increase their phaseshift amounts toward longer wavelengths.

Each element in Groups I and III has L- and M-shell absorption edgesnear the long-wavelength side of the exposure wavelength of 1 to 1.6 nmand decreases its phase shift amount at this absorption edge wavelength.However, in a wavelength region of shorter wavelengths than thisabsorption edge wavelength, a change in the phase shift amount with thewavelength reduces, so the phase dispersion is small in the exposurewavelength region of 0.654 to 1.015 nm. On the other hand, the elementsin Groups II and IV have their absorption edges in the short-wavelengthregion of 0.25 to 0.6 rm of the exposure wavelength. Therefore, changesin the phase shift amounts of these elements with the wavelength arelarger than those of the elements in Groups I and III.

Hence, the elements in Groups I and III are suitable absorber materialsfor controlling the phase shift amount. So, it is possible to improvethe phase shift characteristics of alloys and compounds formed bycombining these elements with the elements in Groups II and IV. Inparticular, Zn and Ga in Group I and Pm Sm, and Eu in Group III aresuitable materials because each element has an absorption edge at 1.1 to1.2 nm near the long-wavelength region of the exposure light, the phasechanges abruptly in the vicinity of 1 nm near this absorption edge, sothe phase shift amount decreases in the long-wavelength region of theexposure light. Zn and Ga in Group I and Pm, Sm, and Eu in Group III candecrease changes in the phase shift amount with the wavelength in theexposure wavelength region when combined with any element in Groups I toIV, which increases the phase shift amount in the long-wavelength regionof the exposure light, in the form of alloys or compounds. Hence, thesecombinations are preferable. In particular, the phase shift deviation ofeach element in Groups II and IV with low phase controllability is|Φ₁-Φ₂|≦π±0.20 to 0.30 π in π phase shift. The characteristics can begreatly improved by combining these elements with the elements in GroupI or the elements in Group III.

For example, the π phase shift angles of an Sm₄Au alloy as thecombination of element Au in Group IV and element Sm in Group III can becontrolled to |Φ₁-Φ₂|≦π±0.04 π. Also, the mask contrast of thisSm_(x)Au_(y) alloy can be made higher than the value of any singleelement. Au has a small film thickness d_(a) of 441.03 nm for π phaseshift and also has high mask contrast. Therefore, the alloy containingAu is an absorber material suited to obtaining high resolution by usingphase shift effect in exposure by synchrotron radiation in thiswavelength region. This also holds true for other elements in Group IV.Os, Pt, and Ir are suitable materials for the alloy because they havelarge absorption than Au.

Accordingly, to change the phase characteristics of the elements inGroups II and IV, which have absorption edges on the short-wavelengthside (0.25 to 0.60 nm), it is effective to form compounds by combiningthese elements with the elements in Groups I and III, which haveabsorption edges at 1 to 1.6 nm. It is also possible to make the maskcontrast higher than the value of any single element because theabsorption characteristic changes.

FIGS. 11A and 11B and Table 12 below show changes in the phase shiftdispersion and the mask contrast (absorber film thickness 0.4 μm) whenthe composition of an Sm_(x)Au_(y) binary alloy is changed. The maskcontrast is a maximum at a composition ratio of Sm₃Au₂, and the phaseshift can also be controlled very accurately, i.e., the controllabilityis π±0.08 π for a film thickness of about 700 nm. Therefore, this alloyis suitable for an absorber material of the X-ray mask.

TABLE 12 Au Sm₂Au₈ Sm₄Au₆ Sm₅Au₅ Sm₆Au₄ Sm₈Au₂ Sm Absorber film 441.03505.40 590.70 642.07 699.09 848.44 1127.20 thickness [nm] Mask contrast5.12(4.40) 7.91(5.23) 12.83(5.80) 16.51(5.95) 21.16(5.99) 35.33(5.69)70.75(4.87) at Si₃N₄ membrane Mask contrast 5.17(4.47) 8.00(5.28)13.01(5.86) 16.76(6.01) 21.50(6.05) 35.96(5.74) 72.24(4.91) at SiCmembrane Mask contrast 4.94(4.29) 7.57(5.05) 12.13(5.60) 15.51(5.75)19.75(5.78) 32.49(5.50) 63.65(4.73) at diamond membrane Mask contrast5.21(4.50) 8.08(5.32) 13.16(5.91) 16.97(6.06) 21.79(6.10) 36.51(5.78)73.54(4.94) at Si membrane Exposure 6.54-10.15 6.54-10.15 6.54-10.156.54-10.15 6.54-10.15 6.54-10.15 6.54-10.15 wavelength region [Å]Deviation Δφ ±0.25 ±0.20 ±0.14 ±0.11 ±0.08 ±0.04 ±0.10 from the π phaseshift [π] Phase shift 0.75 ≦ φ ≦ 1.25 0.80 ≦ φ ≦ 1.20 0.86 ≦ φ ≦ 1.140.89 ≦ φ ≦ 1.11 0.92 ≦ φ ≦ 1.08 0.96 ≦ φ ≦ 1.04 0.90 ≦ φ ≦ 1.09controllability at above absorber film thickness in exposure wavelength[π] Numerical values in the parentheses of mask contrast are obtainedfor an absorber film thickness of 400 nm

The mask contrast and phase shift controllability of the mask can beimproved by the combinations of Groups I and III, Groups I and II, andGroups II and III, as well as the combination of Groups III and IV.

Table 13 below shows the phase shift controllability (in the same fromas in Table 11) and the mask contrast values when alloys and compoundsas principal combinations of Groups I and III, and Groups III and IV,are used as absorber materials.

TABLE 13 Phase shift π phase shift controllability φ[π] Mask Mask MaskMask average film Phase shift deviation contrast contrast contrastcontrast thickness [nm] Δφ[π] Si₃N₄ 1 μm SiC 1 μm C 1 μm Si 1 μmGroup-I- + Group-III- Sm₃Cr₂ 995.44 0.97 ≦ φ ≦ 1.03 27.81 28.28 25.7228.70 Δφ = ±0.03 (4.00) (4.03) (3.90) (4.05) Sm₂Fe₃ 877.54 0.94 ≦ φ ≦1.06 17.71 17.98 16.56 18.23 Δφ = ±0.06 (3.87) (3.90) (3.77) (3.93)Nd₃Co₂ 805.33 0.90 ≦ φ ≦ 1.10 12.97 13.16 12.20 13.32 Δφ = ±0.10 (3.71)(3.79) (3.61) (3.76) SmCo₄ 716.07 0.89 ≦ φ ≦ 1.10 10.22 10.36 9.67 10.48Δφ = ±0.11 (3.80) (3.83) (3.69) (3.86) NdNi 835.88 0.92 ≦ φ ≦ 1.07 16.2616.51 15.19 16.73 Δφ = ±0.08 (3.97) (4.00) (3.86) (4.03) SmNi₄ 702.030.91 ≦ φ ≦ 1.10 11.69 11.86 11.01 12.01 Δφ = ±0.10 (4.23) (4.27) (4.10)(4.30) NdCu 860.47 0.94 ≦ φ ≦ 1.06 18.47 18.77 17.18 19.04 Δφ = ±0.06(4.07) (4.11) (3.96) (4.13) Group-III- + Group-IV- Nd + Group-IV- Nd₇Ir₃701.28 0.89 ≦ φ ≦ 1.11 17.67 17.93 16.64 18.15 Δφ = ±0.11 (5.32) (5.37)(5.16) (5.40) Nd₃Au₂ 678.49 0.88 ≦ φ ≦ 1.12 14.13 14.33 13.30 14.51 Δφ =±0.12 (4.94) (4.98) (4.78) (5.01) Sm + Group-IV- Sm₁₁Ir₉ 623.38 0.89 ≦ φ≦ 1.11 19.60 19.88 18.50 20.13 Δφ = ±0.11 (7.00) (7.06) (6.76) (7.11)SmAu 642.07 0.89 ≦ φ ≦ 1.11 16.51 16.76 15.51 16.97 Δφ = ±0.11 (5.95)(6.01) (5.75) (6.06) Sm₄Au 848.44 0.97 ≦ φ ≦ 1.04 35.33 35.96 32.4936.51 Δφ = ±0.04 (5.69) (5.74) (5.50) (5.78) Eu + Group-IV- Eu₃Ir₂708.16 0.88 ≦ φ ≦ 1.12 23.22 23.60 21.82 23.94 Δφ = ±0.12 (6.26) (6.33)(6.06) (6.38) EuAu 689.36 0.88 ≦ φ ≦ 1.12 12.22 12.39 11.57 12.55 Δφ =±0.12 (5.16) (5.21) (4.99) (5.26) Gd + Group-IV- Gd₁₁Ir₉ 643.21 0.89 ≦ φ≦ 1.11 24.79 25.15 23.43 25.47 Δφ = ±0.11 (7.67) (7.75) (7.42) (7.82)GdPt 627.37 0.90 ≦ φ ≦ 1.11 20.83 21.14 19.57 20.94 Δφ = ±0.11 (7.22)(7.29) (6.96) (7.36) GdAu 661.88 0.90 ≦ φ ≦ 1.10 20.36 20.67 19.14 20.94Δφ = ±0.10 (6.45) (6.51) (6.23) (6.56) Tb + Group-IV- Tb₂Au₃ 606.80 0.88≦ φ ≦ 1.12 14.05 14.22 13.34 14.36 Δφ = ±0.12 (5.88) (5.94) (5.69)(5.97) Numerical values in the parentheses of mask contrast are obtainedfor an absorber film thickness of 400 nm

It is evident from Tables 12 and 13 and FIGS. 11A and 11B that the maskcontrast and the phase shift controllability of an alloy or compound canbe changed by changing the composition ratio, and that a desired maskcontrast and phase shift amount can be accurately controlled by the filmthickness of absorber, by optimizing the composition ratio, and bycombining the materials proposed in this embodiment.

Accordingly, alloys and compounds formed by combining Co(27) to Ga(31)of atomic numbers 27 to 31 in Group I with La(57) to Eu(63) of atomicnumbers 57 to 63 in Group III, alloys formed by combining La(57) toEu(63) of atomic numbers 57 to 63 in Group III with Os(76) to U(92) ofatomic numbers 76 to 92 in Group IV, alloys formed by combining Rh(45)to Ag(47) of atomic numbers 45 to 47 in Group II with Co(27) to Ga(31)of atomic numbers 27 to 31 in Group I or La(57) to Eu(63) of atomicnumbers 57 to 63 in Group III are suitable materials for an absorber ofa phase shift mask for the proximity X-ray lithography using synchrotronradiation with a wavelength region of 0.6 to 1 nm.

Assume that the following three conditions are desirable for a phaseshift mask absorber material having high phase shift controllability, asmall absorber film thickness, and an appropriate mask contrast value:

1) ΔΦ≦0.10 π (0.95≦|cosΦ|≦1)

2) a mask contrast value C is about 10 to 20 for the π phase shift filmthickness

3) π phase shift film thickness d_(a)≦850 nm

Of the abovementioned alloys and compounds, suitable absorber materialsmeeting all these conditions are SmNi₄

π phase absorber film thickness: d_(a)=702.03 nm

(mask contrast: 11.01 to 12.01)

phase shift controllability: |Φ₁-Φ₂|≦π±0.10 π

Nd₂Cu₃

π phase absorber film thickness: d_(a)=813.14 nm

(mask contrast: 14.97 to 16.52)

phase shift controllability: |Φ₁-Φ₂|≦π±0.07 π

Nd₃Cu₇

π phase absorber film thickness: d_(a)=764.23 nm

(mask contrast: 12.81 to 14.08)

phase shift controllability: |Φ₁-Φ₂|≦π±0.08 π

as combinations of Groups I and III, and

Nd₄Au

π phase absorber film thickness: d_(a)=837.64 nm

(mask contrast: 19.50 to 21.59)

phase shift controllability: |Φ₁-Φ₂|≦π±0.08 π

GdAu

π phase absorber film thickness: d_(a)=661.88 nm (mask contrast: 19.14to 20.94)

phase shift controllability: |Φ₁-Φ₂|≦π±0.10 π

as combinations of Groups III and IV.

Absorber materials meeting the aforementioned three conditions can alsobe obtained by composition ratios and combinations other than thosedescribed above. Therefore, it is possible to accurately control adesired mask contrast and phase shift amount for an arbitrary filmthickness by optimizing the composition ratio and by the combinations ofmaterials proposed in the present invention.

(Fifth Embodiment)

In the third and fourth embodiments, suitable absorber materials when notransparent film exists in trenches between absorber patterns areexplained. In this embodiment, an X-ray mask shown in FIGS. 12A to 14Bin which a transparent film having small absorption of X-rays exists ona membrane will be described. A transparent film 8 on a membrane 6 hassmall absorption of an exposure wavelength. As the constituent elementof this material, an element not including an absorption edge in theexposure wavelength region of the exposure light or an element includingan absorption edge near the short-wavelength side of the exposurewavelength region is used. Consequently, it is possible to control thedispersion of a phase shift amount with respect to the wavelength of anabsorber 5.

The invention of a method of controlling the phase shift amount by usingthe above transparent film of this embodiment will be described below.

Let Φ_(a) and Φ_(t) be the phase shift amounts of X-rays transmittedthrough the absorber and the transparent film, respectively, of theX-ray mask shown in FIGS. 12A to 14B.

By selecting a material by which |Φ_(a)-Φ_(t)| has the phase shift Φ_(t)suited to the phase shift Φ_(a) transmitted through the absorber in theexposure wavelength region, the phase shift controllability in exposureusing synchrotron radiation having a wide wavelength band can beincreased.

As the absorber material, an element, or a compound or multi-layer filmcontaining an element all absorption edges of which are shorter than theshortest wavelength, longer than the longest wavelength, or near thelongest wavelength (within 0.1 nm from the longest wavelength) of anexposure wavelength region (a wavelength region having intensity{fraction (1/10)} the light intensity of a maximum light intensitywavelength entering the X-ray mask or more) is suitable for the phaseshift mask. A material containing an element whose absorption edge isincluded in the exposure wavelength region is unsuitable because thephase shift largely changes at the absorption edge wavelength and itsvicinity to increase the phase shift deviation in the exposurewavelength region. This also holds for the transparent film material. Itis desirable to use a element or compound or multi-layer film containingan element all absorption edges of which are shorter than the shortestwavelength or longer than the longest wavelength of the exposurewavelength region, or an element having an absorption edge near theshortest wavelength.

The transparent film material is desirably a material meeting thefollowing conditions:

1) It has a phase shift characteristic that cancels the phase shiftdeviation of the absorber material.

2) It has small absorption and high transmittance of X-rays as theexposure light.

3) It does not make a thickness D_(t) of the transparent film so large.

Condition 1) is to obtain a constant phase shift amount with respect toeach wavelength of synchrotron radiation having a wide wavelength regionand thereby suppress the phase shift deviation. An absorber element notincluding absorption edges in the exposure light wavelength regiondecreases the phase shift amount on the short-wavelength side andincreases it on the long-wavelength side. Therefore, the deviation ofthe phase shift amount can be suppressed by using, as the transparentfilm, an element not including absorption edges in the exposure lightwavelength region or an element having an absorption edge near theshortest wavelength of the exposure wavelength region. An element havingan absorption edge near the shortest wavelength abruptly decreases arefractive index n_(t)(λ_(a)) and Φ_(t)(λ_(a)) at an absorption edgewavelength λ_(a) and increases |Φ_(a)( λ_(a))-Φ_(t)(λ_(a))| in theshort-wavelength region. Consequently, the deviation of the phase shiftamount of the absorber can be suppressed. An element having anabsorption edge within 0.1 nm from the shortest wavelength is desirable.

Condition 2) means that if the absorption by the transparent film islarge, the mask contrast obtained by this mask lowers. Condition 3) hasthe following meaning. If the thickness of the transparent film must beincreased for phase shift, the absorption by the transparent filmincreases. This not only lowers the mask contrast but also increases theaspect ratio of fine patterns formed on the membrane film. Consequently,it is difficult to manufacture the fine-structure and fill the absorbermaterial or the transparent film material in the fine pattern trenches.Condition 4) is necessary when reflow sputtering is used to fill theabsorber material in the fine pattern trenches of the transparent film.

Transparent film materials meeting the above conditions in the X-raymask shown in FIGS. 12A to 14B when synchrotron radiation having anexposure wavelength region of 0.654 to 1.015 nm, i.e., having exactlythe same condition as the exposure condition in the first embodiment arepresented below, and the effects of these materials will be described indetail.

First, when the phase shift difference |Φ_(a)-Φ_(t)| between X-raystransmitted through the absorber and the transparent film, respectivelyis π, the film thicknesses D_(a) and D_(t) of the absorber and thetransparent film, respectively, are represented by

|Φ_(a)-Φ_(t)|=2π|n_(a)D_(a)-n_(t)D_(t)|/λ=mπ  (5)

|n_(a)D_(a)-n_(t)D_(t)|=m(λ/2)

|δ_(a)(λ)D_(a)-δ_(t)(λ)D_(t)|=m(λ/2)

m=0, ±1, ±2,   (6)

where

Φ_(a): the phase shift angle after transmission through the membrane andthe absorber

Φ_(t): the phase shift angle after transmission through the membrane andthe transparent film

n_(a), n_(t): the refractive indices of the absorber and the transparentfilm δ_(a)(λ), δ_(t)(λ): δ_(a)(λ)=1−n_(a), δ(λ)=1−n_(t)

D_(a), D_(t): the film thicknesses of the absorber and the transparentfilm

Film thicknesses required to change the phase shift by π for variouselements, alloys, and compounds are calculated to examine the wavelengthdispersion of the phase shift. The wavelength region is 0.654 to 1.015nm from the maximum intensity to the {fraction (1/10)} intensity in theintensity spectrum of the synchrotron radiation after transmissionthrough the membrane (1.0 μm thick). Letting d_(a) and d_(t) be the πphase shift average film thicknesses of the absorber and the transparentfilm, respectively, in the exposure light wavelength band of 0.654 to1.015 nm, and P be the difference |Φ_(a)-Φ_(t)| between the phase shiftamounts after transmission through the absorber and the transparent filmhaving the thicknesses D_(a) and D_(t), respectively, we have

D_(a)/d_(a)-D_(t)/d_(t)=P/π  (7)

where

D_(a), D_(t): the thicknesses of the absorber and the transparent film

d_(a): the π phase shift average film thickness of the absorber in theexposure light wavelength region

d_(t): the π phase shift average film thickness of the transparent filmin the exposure light wavelength region

P: P=|Φ_(a)-Φ_(t)| phase shift amount

Therefore, if the film thicknesses of the absorber and the transparentfilm are equal (FIGS. 12A to 12C), the film thickness for the phaseshift amount P is D_(a)=D_(t) (≡D). This film thickness D is representedby

D=(d_(a)d_(t)/|d_(t)-d_(a)|)·P/π  (8)

The phase shift deviation in this exposure wavelength region isrepresented by

ΔΦ_(D)=D·(ΔΦ_(a)/d_(a)—ΔΦ_(t)/d_(t))  (9)

ΔΦ_(D)=(d_(a)d_(t)/|d_(t)-d_(a)|)·(P/π)·(ΔΦ_(a)/d_(a)−ΔΦ_(t)/d_(t))=(P/π|d_(t)−d_(a)|)·(d_(t)ΔΦ_(a)−d_(a)ΔΦ_(t))  (9′)

If the film thickness of the absorber and the transparent film aredifferent (D_(a)≠D_(t)) (FIGS. 13A to 14B), we have

ΔΦ_(D)=ΔΦ_(a)D_(a)/d_(a)−ΔΦ_(t)D_(t)/d_(t)  (10)

where

ΔΦ_(a): the maximum deviation in the exposure wavelength from the phaseπ for the π phase shift average film thickness d_(a) of the absorber

ΔΦ_(t): the maximum deviation in the exposure wavelength from the phaseπ for the π phase shift average film thickness d_(t) of the transparentfilm

ΔΦ_(D): the maximum deviation in the exposure wavelength from the phaseπ for the π phase shift average film thickness D

Equations (9) and (10) hold only for materials in which the absorptionedges of constituent elements of the absorber and transparent filmmaterials do not exist in the exposure light wavelength region of 0.654to 1.015 nm. In this embodiment, the phase characteristics and theabsorption characteristics of combinations of various materials of theabsorber and the transparent film when the film thicknesses of theabsorber and the transparent film are equal (D_(a)=D_(t) (≡D)) will bechecked to examine combinations of absorber materials and transparentfilm materials suited to the phase shift mask.

First, assume that practical conditions of conditions 1) and 2)previously enumerated as desirable conditions of the transparent filmmaterial are as follows:

1) An element all absorption edges of which are shorter than theshortest wavelength or longer than the longest wavelength of theexposure wavelength, or an element having an absorption edge within 0.1nm from the shortest wavelength (Si: K 0.6738 nm and Rb: L3 0.6862 nm).

2) A material having small absorption and an attenuation of the lightintensity of transmitted light of exposure light of 50% or less when thefilm thickness D_(t) is 400 nm. Table 14 below shows the characteristicsof elements meeting these two conditions.

TABLE 14 Phase shift characteristics of elements used in transparentfilm material Melting Phase shift π phase shift Atomic point deviationfilm thickness Δφ_(t)/d_(t) × 10⁻⁵ number [° C.] Δφ_(t) [π] d_(t) [nm][π/nm] Be 4 1278 0.22 2639.8 8.33 B 5 2300 0.23 11171.9 2.06 C 6 35500.23 1216.3 18.91 N 7 −210 0.22 3721.3 5.91 O 8 −218 0.22 2716.6 8.10 F9 −220 0.21 3037.8 6.91 Na 11 97.81 0.13 5161.5 2.52 Si 14 1414 0.392402.2 16.24 P 15 589.5 0.26 2799.8 9.29 S 16 112.8 0.24 2314.7 10.37 Cl17 −101 0.23 2222.1 10.35 K 19 63.5 0.23 5419.7 4.24

TABLE 14 Phase shift characteristics of elements used in transparentfilm material Melting Phase shift π phase shift Atomic point deviationfilm thickness Δφ_(t)/d_(t) × 10⁻⁵ number [° C.] Δφ_(t) [π] d_(t) [nm][π/nm] Ca 20 848 0.23 2923.8 7.87 Sc 21 1541 0.22 1574.8 13.97 Ti 221675 0.22 1089.2 20.20 V 23 1890 0.21 849.6 24.72 Cr 24 1890 0.21 677.930.98 Rb 37 38.89 0.41 4903.5 8.36 Sr 38 769 0.36 2701.7 13.32 Y 39 14950.28 1431.7 19.56 Zr 40 1852 0.26 960.9 27.06 Nb 41 2468 0.24 713.033.66 Mo 42 2610 0.23 596.6 38.55 I 53 113.6 0.16 1272.3 12.58 Ra 88 7000.16 1671.6 9.57

Accordingly, Be, B, C, N, O, F, Na, Si, P, S, Cl, K, Ca, Sc, Ti, V, Cr,Rb, Sr, Y, Zr, Nb, Mo, I, and Ra are suitable for constituent elementsof the transparent film material when synchrotron radiation having anexposure wavelength region between 0.65 nm and 1.02 nm is used as anexposure light source.

This Table 14 shows the melting point, the π shift average filmthickness d_(t), the maximum deviation ΔΦ_(a) from the phase π for thisfilm thickness, and the maximum deviation ΔΦ_(a)/d_(a) of a phase shiftper unit thickness of each element.

Analogously, Table 15 below shows the melting point, the π shift averagefilm thickness d_(a), the maximum deviation ΔΦ_(a) from the phase π forthis film thickness, and the maximum deviation ΔΦ_(a)/d_(a) of a phaseshift per unit thickness of each of various principal elements having noabsorption edges in the exposure wavelength region and suitable for theabsorber material of the phase shift mask.

TABLE 15 Phase shift characteristics of elements used in transparentfilm material Melting Phase shift π phase shift Atomic point deviationfilm thickness Δφ_(t)/d_(t) × 10⁻⁵ number [° C.] Δφ_(t) [π] d_(t) [nm][π/nm] Co 27 1494.0 0.18 586.3 30.70 Ni 28 1455.0 0.16 5665 28.24 Cu 291084.5 0.13 612.4 21.23 Zn 30 419.6 0.10 790.2 12.65 Tc 43 2170.0 0.22523.4 42.03 Ru 44 2250.0 0.22 491.5 44.76 Rh 45 1963.0 0.22 474.1 46.40Pd 46 1554.0 0.21 487.5 43.08 Ag 47 961.4 0.21 556.0 37.71 Cd 48 321.10.20 691.5 28.92 In 49 156.6 0.20 823.9 24.27 Sn 50 232.0 0.19 831.522.85 Sb 51 630.7 0.19 910.5 20.87 Hg 80 −38.9 0.24 618.2 38.82 T1 81302.5 0.22 701.2 31.37 Pb 82 327.5 0.21 731.7 28.70 Bi 83 271.4 0.20833.4 24.00 Po 84 254.0 0.19 887.6 21.41 At 85 302.0 0.18 803.0 22.42 Rn86 −71.0 0.17 841.4 20.21 Fr 87 27.0 0.17 828.4 20;52 Ac 89 1050.0 0.16816.9 19.59 Th 90 1750.0 0.14 732.6 19.11 Pa 91 1840.0 0.12 857.6 13.99U 92 1133.0 0.14 443.3 31.58

When synchrotron radiation having an exposure wavelength region between0.65 nm and 1.02 nm is used as an exposure light source, suitableabsorber materials are elements having large absorption of X-rays inthis wavelength region, among other elements listed in Table 15.Elements whose exposure light transmittance is 25% or less for anabsorber film thickness of 400 nm are Co, Ni, Cu, Zn, Ga, Rh, Pd, Ag,La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Pt, and Au. Accordingly, theseelements and alloys are suitable absorber materials for an X-ray maskhaving a transparent film on a membrane when synchrotron radiationhaving an exposure wavelength region between 0.65 nm and 1.02 nm is usedas an exposure light source.

Of the above suitable elements,

a) Au (ΔΦ_(a)=0.25 π, d_(a)=441.0 nm)

b) Cu (ΔΦ_(a)=0.13 π, d_(a)=612.4 nm)

c) Ni (ΔΦ_(a)=0.16 π, d_(a)=566.1 nm)

were used as absorber materials of an X-ray mask with a transparentfilm, and the phase shift characteristics for various transparent filmswere substituted into equations (8) and (9). Tables 16 to 18 below showthe results of calculations.

TABLE 16 Phase shift characteristics when Au is combined with varioussingle-element transparent film π phase Melting Phase shift shift filmAtomic point deviation thickness Δφ_(t)/d_(t) × 10⁻⁵ number [° C.]Δφ_(t) [π] d_(t) [nm] [π/nm] D [nm] Δφ_(D)[π] *Si 14 1414 0.39 2402.2016.24 540.21 0.219 *Sr 38 769 0.36 2701.70 13.32 527.07 0.229 *Rb 3738.89 0.41 4903.50 8.36 484.62 0.234 *Y 39 1495 0.28 1431.70 19.56637.37 0.237 *Zr 40 1852 0.26 960.90 27.06 815.18 0.242 P 15 589.5 0.262799.80 9.29 523.49 0.248 B 5 2300 0.23 11171.90 2.06 459.16 0.251 Li 3179 0.22 9522.90 2.31 462.45 0.251 K 19 63.5 0.23 5419.70 4.24 480.100.252 S 16 112.8 0.24 2314.70 10.37 544.84 0.252 Ca 20 848 0.23 2923.807.87 519.37 0.254 N 7 −210 0.22 3721.30 5.91 500.33 0.254 Cl 17 −1010.23 2222.10 10.35 550.24 0.255 O 8 −218 0.22 2716.60 8.10 526.51 0.256Be 4 1278 0.22 2639.80 8.33 529.49 0.256 F 9 −220 0.21 3037.80 6.91515.93 0.257 Na 11 97.81 0.13 5161.50 2.52 482.24 0.261 C 6 3550 0.231216.30 18.91 691.92 0.261 Sc 21 1541 0.22 1574.80 13.97 612.59 0.262 Nb41 2468 0.24 713.00 33.66 1156.21 0.266 Ti 22 1675 0.22 1089.20 20.20741.12 0.270 Ra 88 700 0.16 1671.60 9.57 599.09 0.282 V 23 1890 0.21849.60 24.72 917.10 0.293 I 53 113.6 0.16 1272.30 12.58 675.02 0.298 Mo42 2610 0.23 596.60 38.55 1691.32 0.307 Cr 24 1890 0.21 677.90 30.981262.19 0.324

TABLE 17 Phase shift characteristics when Cu is combined with varioussingle-element transparent film π phase Melting Phase shift shift filmAtomic point deviation thickness Δφ_(t)/d_(t) × 10⁻⁵ number [° C.]Δφ_(t) [π] d_(t) [nm] [π/nm] D [nm] Δφ_(D)[π] Cr 24 1890 0.21 677.9030.98 6338.11 −0.618 Nb 41 2468 0.24 713.00 33.66 4340.37 −0.540 Zr 401852 0.26 960.90 27.06 1688.54 −0.098 V 23 1890 0.21 849.60 24.722193.49 −0.077 Ti 22 1675 0.22 1089.20 20.20 1398.96 0.014 Y 39 14950.28 1431.70 19.56 1070.15 0.018 C 6 3550 0.23 1216.30 18.91 1233.420.029 Si 14 1414 0.39 2402.20 16.24 821.94 0.041 Sr 38 769 0.36 2701.7013.32 791.90 0.063 Sc 21 1541 0.22 1574.80 13.97 1002.09 0.073 Rb 3738.89 0.41 4903.50 8.36 699.80 0.090 S 16 112.8 0.24 2314.70 10.37832.71 0.090 Cl 17 −101 0.23 2222.10 10.35 845.38 0.092 P 15 589.5 0.262799.80 9.29 783.85 0.094 I 53 113.6 0.16 1272.30 12.58 1180.72 0.102 Be4 1278 0.22 2639.80 8.33 797.38 0.103 Ca 20 848 0.23 2923.80 7.87 774.650.104 O 8 −218 0.22 2716.60 8.10 790.63 0.104 F 9 −220 0.21 3037.80 6.91767.03 0.110 N 7 −210 0.22 3721.30 5.91 733.03 0.112 Ra 88 700 0.161671.60 9.57 966.47 0.113 K 19 63.5 0.23 5419.70 4.24 690.41 0.117 Li 3179 0.22 9522.90 2.31 654.49 0.124 B 5 2300 0.23 11171.90 2.06 647.920.124 Na 11 97.81 0.13 5161.50 2.52 694.84 0.130 Mo 42 2610 0.23 596.6038.55 23123.91 4.006

TABLE 18 Phase shift characteristics when Ni is combined with varioussingle-element transparent film π phase Melting Phase shift shift filmAtomic point deviation thickness Δφ_(t)/d_(t) × 10⁻⁵ number [° C.]Δφ_(t) [π] d_(t) [nm] [π/nm] D [nm] Δφ_(D)[π] Mo 42 2610 0.23 596.6038.55 11228.37 −1.157 Nb 41 2468 0.24 713.00 33.66 2757.10 −0.149 Cr 241890 0.21 766.90 30.98 3447.31 −0.094 Zr 40 1852 0.26 960.90 27.061380.20 0.016 V 23 1890 0.21 849.60 24.72 1700.10 0.060 Y 39 1495 0.281431.70 19.56 937.42 0.081 Si 14 1414 0.39 2402.20 16.24 741.32 0.089 Ti22 1675 0.22 1089.20 20.20 1180.47 0.095 C 6 3550 0.23 1216.30 18.911060.38 0.099 Sr 38 769 0.36 2701.70 13.32 716.80 0.107 Sc 21 1541 0.221574.80 13.97 884.78 0.126 Rb 37 38.89 0.41 4903.50 8.36 640.50 0.127 S16 112.8 0.24 2314.70 10.37 750.07 0.134 P 15 589.5 0.26 2799.80 9.29710.20 0.135 Cl 17 −101 0.23 2222.10 10.35 760.34 0.136 Ca 20 848 0.232923.80 7.87 702.64 0.143 Be 4 1278 0.22 2639.80 8.33 721.29 0.144 O 8−218 0.22 2716.60 8.10 715.76 0.144 F 9 −220 0.21 3037.80 6.91 696.360.149 N 7 −210 0.22 3721.30 5.91 668.23 0.149 K 19 63.5 0.23 5419.704.24 632.63 0.152 Li 3 179 0.22 9522.90 2.31 602.33 0.156 B 5 2300 0.2311171.90 2.06 596.76 0.156 I 53 113.6 0.16 1272.30 12.58 1021.19 0.160Ra 88 700 0.16 1671.60 9.57 856.90 0.160 Na 11 97.81 0.13 5161.50 2.52636.34 0.164

The phase shift characteristics when materials a) to c) are used as theabsorber material will be described below.

a) Phase shift characteristics when Au absorber is combined with variouselement transparent films

In Table 16, ΔΦ_(D) indicates the maximum deviation from π in theexposure wavelength region, and elements are arranged in ascending orderof this value. This characteristic is best when Au is combined with Si,and deteriorates in the order of Sr. Rb, Y, Zr, P, and B. In the case ofSi (and Rb), the K-absorption edge exists in the short-wavelength regionof the exposure wavelength region. Therefore, the results are slightlydifferent from the results of equation (9), i.e., D=547.46 nm andΔΦ_(D)=0.235 π in practice. So, Sr is the best material when combinedwith Au. Au has a large maximum deviation ΔΦ_(a)/d_(a) of phase shiftper unit thickness. Hence, it is difficult to largely change thecharacteristics simply by improving the phase shift characteristicΔΦ_(a) from 0.25 to 0.22 π. The characteristics of elements are alsoeffective to evaluate the characteristics of compounds containing theseelements. D and ΔΦ_(D) are the average values of constituent elements(Table 19).

Accordingly, transparent materials by which the thicknesses D of thetransparent film and the absorber are small (D≦1 μm), ΔΦ_(D) is small,and the melting point is high (≧1,500° C.) are probably Si, Zr, SrO,SiO₂, SrS, Y_(x)Si_(y), SiP, Sr₃P₂, ZrP, ZrSi, Y₂O₃, and Y_(x)S_(y).

b) Phase shift characteristics when Cu absorber is combined with variouselement transparent films In Table 17, as in the case of Au, ΔΦ_(D)indicates the maximum deviation from π in the exposure wavelengthregion, and elements are arranged in ascending order of this value. Thischaracteristic is best when Cu is combined with Ti, and deteriorates inthe order of Y, C, Si, Sr, Sc, and V. Cu has a small maximum deviationΔΦ_(a) /d_(a) of phase shift per unit thickness. So, it is possible touse all elements except Mo in Table 17 and readily improve phase shiftcharacteristic ΔΦ_(a)=0.13 π.

Accordingly, transparent materials by which the thicknesses D of thetransparent film and the absorber are small (D≦f 1 μm), ΔΦ_(D) is small,and the melting point is high (≧1,500° C.) are probably Si, SiO₂, SrO,SrS, Y_(x)Si_(y), SiP, and Sr₃P₂.

c) Phase shift characteristics when Ni absorber is combined with variouselement transparent films

In Table 18, as in Tables 16 and 17, ΔΦ_(D) indicates the maximumdeviation, and elements are arranged in ascending order of this value.This characteristic is best when Ni is combined with V, and deterioratesin the order of Y, C, Si, Cr, Ti, and C. Similar to Cu, Ni has a smallmaximum deviation ΔΦ_(a)/d_(a) of phase shift per unit thickness. So, itis possible to use all elements except Na in Table 17 and readilyimprove phase characteristic ΔΦ_(a)=0.16 π.

Accordingly, transparent film materials by which the thicknesses D ofthe transparent film and the absorber are small (D≦1 μm), ΔΦ_(D) issmall, and the melting point is high (≧1,500° C.) are presumably Si,SiC, Si₃N₄, SiO₂, SrO, SrS, Y_(x)Si_(y), SiP, and Sr₃P₂.

From the above results, it is easy from equation (9) to find elements ofthe transparent film material, which decrease the phase shift dispersionwith respect to the exposure wavelength, for various absorbers nothaving absorption edges in the exposure wavelength region. Elementswhich decrease the phase shift dispersion of an absorber or compounds ormultilayered films formed by combining these elements are presumablysuitable for the transparent film material.

Table 19 shows the phase shift characteristics of each transparent filmmaterial when π phase shift was actually performed under the followingconditions:

Absorber materials: Au, Cu, and Ni

Phase shift amount: π

Transparent films: SiO₂, SrO, SrF₂, SiC, Si, MgO, Al₂O₃, and TiO₂

Light source: synchrotron radiation (exposure wavelength region: 0.654to 1.015 nm)

TABLE 19 Transparent Transparent Transparent Transparent TransparentTransparent film none film SiO₂ film SrO film SrF₂ film SiC film Si Au|Δφ_(D)|≦0.25 π |Δφ_(D)|≦0.245 π |Δφ_(D)|≦0.22 π |Δφ_(D)|≦0.23 π|Δφ_(D)|≦0.235 π |Δφ_(D)|≦0.235 π 441.03 nm 556.44 nm 611.47 nm 636.95nm 608.42 nm 547.46 nm Cu |Δφ_(D)|≦0.13 π |Δφ_(D)|≦0.09 π |Δφ_(D)|≦0.04π |Δφ_(D)|≦0.04 π |Δφ_(D)|≦0.065 π |Δφ_(D)|≦0.08 π 612.40 nm 843.01 nm968.98 nm 1035.7 nm 952.17 nm 823.93 nm Ni |Δφ_(D)|≦0.16 π|Δφ_(D)|≦0.125 π |Δφ_(D)|≦0.07 π |Δφ_(D)|≦0.075 π |Δφ_(D)|≦0.10 π|Δφ_(D)|≦0.11 π 566.50 nm 776.97 nm 886.06 nm 941.54 nm 876.00 nm 758.02nm

Table 19 shows that, of transparent film materials not having absorptionedges in the exposure wavelength region, the phase shift deviation|ΔΦ_(D)| improves when elements found to be suited to the compensationof phase shift deviation in Tables 16 to 18 or compounds formed bycombining these elements are used as transparent films. The phase shiftcharacteristics of Cu and Ni absorbers greatly improve by transparentfilms, and that of Au does not improve very much. The results agree wellwith the results shown in Tables 16 to 18.

Of the transparent film materials not having absorption edges in theexposure wavelength region, however, |ΔΦ_(D)| does not improve byelements found to be unsuitable for the compensations of phase shiftdeviation in Tables 16 to 18 or compounds formed by combining theseelements (e.g., a TiO₂ fill structure in Au). Also, the transparent filmthickness of the mask with these transparent films must be larger thanthose of SiO₂, SrO, SiC, and Si transparent film materials. In fillstructures of transparent film materials MgO (Mg: K absorption edge0.9512 nm) and Al₂O₃ (Al: K absorption edge 0.7948 nm) having absorptionedges in the exposure wavelength region, the phase shift characteristic|ΔΦ_(D)| does not improve regardless of the type of absorber materials(Table 20).

TABLE 20 Phase shift characteristics of fill structures of transparentfilm materials MgO and Al₂O₃ *No trans- MgO trans- Al₂O₃ trans- parentfilm parent film parent film |Δφ_(D)|[π] |Δφ_(D)|[π] |Δφ_(D)|[π] Au 0.250.31 0.28 Cu 0.125 0.21 0.12 Ni 0.16 0.23 0.145

From the foregoing, SiO2, SrO, SiC, and Si transparent film materialsare suited to Au, Cu, and Ni absorbers. The SrO film best improves thephase shift characteristics |ΔΦ_(D)| of the Au, Cu, and Ni absorbers,i.e., improves them to 0.22, 0.04, and 0.07 π, respectively. The SiO₂,SiC, and Si films excellently decrease the film thickness (Table 19).

In this embodiment, the phase shift characteristics are evaluated byusing transparent films when the film thicknesses of the absorber andthe transparent film are equal (D_(a)=D_(t) (≡D)). However, theevaluations are readily possible by using equation (9) or (10) even whenthe absorber and the transparent film have different film thicknesses asshown in FIGS. 13A to 14B or when the second transparent film is formedas shown in FIGS. 12B, 12C, 13B, and 14B. The present inventionobviously has the same phase compensating effect in either case.

(Sixth Embodiment)

The fifth embodiment shows that a material having the phase compensatingeffect meeting the absorber material must be chosen as the transparentfilm material. However, it is also important not to decrease the maskcontrast by using a material with small absorption and hightransmittance of X-rays of exposure light used. FIGS. 15 to 19 show thetransmittances to wavelengths of 0.2 to 1.2 nm of the followingtransparent films having the phase compensating effect (for comparison,the transmittance of an SiO₂ film (film thickness 1 μm) is included ineach graph).

That is, FIG. 15 shows the transmittance spectra of Si₃N₄, SiC, Si, anddiamond films (film thickness 1 μm). FIG. 16 shows the transmittances ofMg, Al, Si, and their oxide materials (atomic numbers: 12 to 14), i.e.,Mg, Al, Si, MgO, Al₂O₃, and SiO₂ films (film thickness 1 μm). FIG. 17shows the transmittances of Ca, Sc, Ti, and their oxide materials(atomic numbers: 20 to 22), i.e., Ca, Sc, Ti, CaO, Sc₂O₃, and TiO₂ film(film thickness 1 μm). FIG. 18 shows the transmittances of Sr and itscompound materials (atomic number: 38), i.e., Sr, SrO, and SrF₂ films(film thickness 1 μm). FIG. 19 shows the transmittances of Y, Zr, andtheir compound materials (atomic numbers: 39 and 40), i.e., Y, Zr, Y₂O₃,and ZrO₂ films (film thickness 1 μm).

Table 21 below shows the phase shift characteristics and melting pointsof the materials shown in FIGS. 15 to 19.

TABLE 21 Characteristics of principal elements and compounds astransparent film materials π phase shift Deviation Phase shift averagefilm from phase change rate Absorption Melting thickness shift πΔφ_(t)/d_(t) edge Density point d_(t)[nm] Δφ_(t)[π] × 10⁻⁴[π/nm] [A][g/cm³] [° C.] C 1216.3 0.225 1.85 C K: 43.68 3.51 >3800 (diamond) Mg3722.2 0.28 0.752 Mg K: 9.512 1.74 649 Mg K: 9.512 MgO 1351.4 0.13 1.30O K: 23.32 3.58 2642 Al 2125.0 0.30 1.41 Al K: 7.948 2.69 660 Al₂O₃1156.1 0.20 1.73 Al K: 7.948 4.00 2049 O K: 23.32 Si 2402.2 0.39 1.62 SiK: 6.738 2.34 1414 SiO₂ 2150.5 0.28 1.30 Si K: 6.738 2.22 1713 O K:23.32 Si₃N₄ 1449.3 0.26 1.86 Si K: 6.738 3.44 1900 N K: 30.99 SiC 1666.70.32 1.92 Si K: 6.738 3.10 2827 C K: 43.68 Ca 2923.8 0.23 0.787 Ca K:3.070 1.55 848 CaO 1766.0 0.22 1.25 Ca K: 3.070 3.25 2707 O K: 23.32 Sc1574.8 0.22 1.40 Sc K: 2.762 3.02 1575 Sc₂O₃ 1187.8 0.22 1.85 Sc K:2.762 3.88 >2405 O K: 23.32 Ti 1089.2 0.22 2.02 Ti K: 2.497 4.50 1675TiO₂ 1204.8 0.22 1.83 Ti K: 2.497 3.84 1839 O K: 23.32 Sr 2701.7 0.361.33 Sr L: 5.59-6.39 2.62 769 SrO 1574.8 0.32 2.03 Sr L: 5.59-6.39 4.082430 O K: 23.32 SrF₂ 1425.2 0.295 2.07 Sr L: 5.59-6.39 4.24 1463 F K:18.00 SrS 1704.7 0.315 1.85 Sr L: 5.59-6.39 3.70 >2000 S K: 5.019 Y1431.7 0.28 1.96 Y L: 5.22-5.96 4.48 1495 Y₂O₃ 1204.2 0.26 2.16 Y L:5.22-5.96 4.84 2230-2680 O K: 23.32 YSi 1353.1 0.285 2.11 Y L: 5.22-5.964.53 1870 Si K: 6.738 Zr 960.9 0.26 2.71 Zr L: 4.88-5.58 6.53 1852 ZrO₂953.8 0.24 2.52 Zr L: 4.88-5.58 5.85 2670 O K: 23.32

The transmittances and melting points shown in Table 21 indicate thatSi, Si₃N₄, SiC, SiO₂, and SrO films are good transparent film materialsin the exposure wavelength region of 0.7 to 1.2 nm, and diamond, CaO,Sc₂O₃, and TiO₂ films are good transparent film materials in theexposure wavelength region of 0.3 to 0.7 nm.

Tables 22 to 24 below show the mask contrasts when the above transparentfilms are combined with Au, Cu, and Ni absorbers.

TABLE 22 Phase shift and mask contrast characteristics of the X-ray maskwith Au absorber buried into the various transparent film pattern Si₃N₄SiC Diamond Si membrane membrane membrane membrane (1 μm) (1 μm) (1 μm)(1 μm) Phase shift Mask Mask Mask Mask controllability and Average filmcontrast contrast contrast contrast deviation from thickness da M @ da(M@ d = M @ da(M @ d = M @ da(M @ d = M @ da(M @ d = phase shift π [nm]0.4 μm) 0.4 μm) 0.4 μm) 0.4 μm) *Au 0.75 π ≦ φ ≦ 1.25 π 441.03 5.12 5.174.94 5.21 |Δφ_(D)|≦0.25 π (4.40) (4.47) (4.29) (4.50) Au—SiO₂ 0.75 π ≦ φ≦ 1.24 π 556.44 6.72 6.81 6.40 6.88 |Δφ_(D)|≦0.245 π (4.03) (4.07)(3.90) (4.10) Au—SrO 0.78 π ≦ φ ≦ 1.24 π 611.47 6.70 6.78 6.36 6.85|Δφ_(D)|≦0.22 π (3.58) (3.61) (3.46) (3.63) Au—SrF₂ 0.77 π ≦ φ ≦ 1.23 π636.95 6.87 6.95 6.52 7.02 |Δφ_(D)|≦0.23 π (3.47) (3.50) (3.37) (3.52)Au—SiC 0.76 π ≦ φ ≦ 1.24 π 608.42 8.13 8.24 7.65 8.34 |Δφ_(D)|≦0.24 π(4.09) (4.13) (3.93) (4.17) Au—Si 0.76 π ≦ φ ≦ 1.23 π 547.46 6.84 6.936.47 7.01 |Δφ_(D)|≦0.235 π (4.17) (4.21) (4.00) (4.24) Au—MgO 0.69 π ≦ φ≦ 1.31 π 647.02 5.73 5.80 5.49 5.86 |Δφ_(D)|≦0.31 π (3.04) (3.07) (2.97)(3.09) Au—Al₂O₃ 0.72 π ≦ φ ≦ 1.28 π 713.38 7.83 7.97 7.39 8.09|Δφ_(D)|≦0.28 π (3.31) (3.34) (3.21) (3.37) Au—TiO₂ 0.73 π ≦ φ ≦ 1.27 π696.64 7.93 8.02 7.56 8.10 |Δφ_(D)|≦0.27 π (3.42) (3.45) (3.34) (3.47)

TABLE 23 Phase shift and mask contrast characteristics of the X-ray maskwith Cu absorber buried into the various transparent film pattern Si₃N₄SiC Diamond Si membrane membrane membrane membrane (1 μm) (1 μm) (1 μm)(1 μm) Phase shift Mask Mask Mask Mask controllability and Average filmcontrast contrast contrast contrast deviation from thickness da M @ da(M@ d = M @ da(M @ d = M @ da(M @ d = M @ da(M @ d = phase shift π [nm]0.4 μm) 0.4 μm) 0.4 μm) 0.4 μm) *Cu 0.88 π ≦ φ ≦ 1.13 π 612.40 7.57 7.687.19 7.77 |Δφ_(D)|≦0.125 π (3.89) (3.93) (3.77) (3.97) Cu—SiO₂ 0.91 π ≦φ ≦ 1.09 π 843.01 12.40 12.62 11.43 12.81 |Δφ_(D)|≦0.09 π (3.55) (3.58)(3.42) (3.61) Cu—SrO 0.96 π ≦ φ ≦ 1.04 π 968.98 13.07 13.30 11.94 13.51|Δφ_(D)|≦0.04 π (3.15) (3.18) (3.04) (3.20) Cu—SrF₂ 0.96 π ≦ φ ≦ 1.04 π1035.7 14.14 14.39 12.86 14.62 |Δφ_(D)|≦0.04 π (3.05) (3.08) (2.96)(3.10) Cu—SiC 0.93 π ≦ φ ≦ 1.06 π 952.17 17.22 17.58 15.53 17.89|Δφ_(D)|≦0.065 π (3.60) (3.64) (3.46) (3.67) Cu—Si 0.92 π ≦ φ ≦ 1.08 π823.93 12.64 12.88 11.54 13.09 |Δφ_(D)|≦0.08 π (3.67) (3.71) (3.52)(3.74) Cu—MgO 0.79 π ≦ φ ≦ 1.21 π 1003.8 9.56 9.74 8.88 9.89|Δφ_(D)|≦0.21 π (2.68) (2.70) (2.61) (2.72) Cu—Al₂O₃ 0.88 π ≦ φ ≦ 1.12 π1194.2 17.66 18.15 15.82 18.58 |Δφ_(D)|≦0.12 π (2.91) (2.94) (2.82)(2.97) Cu—TiO₂ 0.93 π ≦ φ ≦ 1.08 π 1189.2 19.12 19.46 17.40 19.76|Δφ_(D)|≦0.075 π (2.74) (2.76) (2.93) (3.06)

TABLE 24 Phase shift and mask contrast characteristics of the X-ray maskwith Ni absorber buried into the various transparent film pattern Si₃N₄SiC Diamond Si membrane membrane membrane membrane (1 μm) (1 μm) (1 μm)(1 μm) Phase shift Mask Mask Mask Mask controllability and Average filmcontrast contrast contrast contrast deviation from thickness da M @ da(M@ d = M @ da(M @ d = M @ da(M @ d = M @ da(M @ d = phase shift π [nm]0.4 μm) 0.4 μm) 0.4 μm) 0.4 μm) *Ni 0.84 π ≦ φ ≦ 1.16 π 566.51 5.77 5.845.52 5.91 |Δφ_(D)|≦0.16 π (3.54) (3.57) (3.43) (3.60) Ni—SiO₂ 0.88 π ≦ φ≦ 1.13 π 776.97 8.73 8.87 8.15 8.99 |Δφ_(D)|≦0.125 π (3.22) (3.25)(3.12) (3.28) Ni—SrO 0.93 π ≦ φ ≦ 1.07 π 886.06 8.86 9.00 8.21 9.12|Δφ_(D)|≦0.07 π (2.86) (2.89) (2.77) (2.91) Ni—SrF₂ 0.92 π ≦ φ ≦ 1.07 π941.54 9.32 9.47 8.62 9.60 |Δφ_(D)|≦0.075 π (2.78) (2.80) (2.69) (2.82)Ni—SiC 0.90 π ≦ φ ≦ 1.10 π 876.00 14.58 11.80 10.60 11.99 |Δφ_(D)|≦0.10π (3.27) (3.31) (3.15) (3.33) Ni—Si 0.89 π ≦ φ ≦ 1.11 π 758.02 8.87 9.028.21 9.16 |Δφ_(D)|≦0.11 π (3.33) (3.37) (3.20) (3.40) Ni—MgO 0.77 π ≦ φ≦ 1.23 π 912.64 6.55 6.66 6.17 6.75 |Δφ_(D)|≦0.23 π (2.43) (2.45) (2.38)(2.47) Ni—Al₂O₃ 0.86 π ≦ φ ≦ 1.15 π 1086.67 11.19 11.46 10.22 11.70|Δφ_(D)|≦0.145 π (2.65) (2.68) (2.57) (2.70) Ni—TiO₂ 0.89 π ≦ φ ≦ 1.11 π1070.27 11.77 11.95 10.91 12.10 |Δφ_(D)|≦0.11 π (2.74) (2.76) (2.67)(2.78)

SrF₂, MgO, Al₂O₃, and TiO₂ films are unsuitable because the maskcontrast of each film drops to 80% or less compared to a case wherethere is no transparent film, and the film thickness of each film mustbe larger than those of SiO₂, SrO, SiC, and Si transparent filmmaterials. Accordingly, SiO₂, SrO, SiC, and Si are suitable transparentfilm materials having high transmittance in the wavelength region of 0.6to 1 nm and a good phase shift characteristic with respect to anabsorber material having large absorption in this wavelength region.

(Seventh Embodiment)

In the fifth and sixth embodiments, elements and compounds composed oftransparent films which decrease the phase shift deviation when Au, Cu,and Ni are used as absorber materials are described. However, it is easyfrom equations (9) and (10) to find elements having phase compensatingeffect with respect to other various absorbers. The phase shiftdeviation of X-ray mask can decrease when elements found by equations(9) and (10) to compensate for the phase shift deviation of an absorber,or compounds, or multilayered films formed by combining these elementsare used as transparent film materials.

Accordingly, an X-ray mask with an absorber buried into the patternedtransparent film is expected to suppress deterioration of the resolutioncaused by diffraction by the phase shift effect even in a proximityX-ray lithography using synchrotron radiation. In particular, a maskwith an SiO₂ transparent film is effective as a phase shift mask forX-ray exposure having a wavelength region of 0.6 to 1 nm. Additionally,this mask can be easily manufactured by the existing semiconductorprocess technologies. Therefore, this mask is presumably one optimumphase shift mask for synchrotron radiation exposure.

The results of π phase shift of the X-ray mask indicate that when SiO₂,ZrO, SrF₂, SiC, and Si are used as transparent films, |ΔΦ| improves from0.16 π to 0.07 to 0.125 π, from 0.125 π to 0.04 to 0.09 π, and from 0.25π to 0.22 to 0.245 π for Ni, Cu, and Au, respectively. Especially whenthese absorber materials are filled in SrO patterns, the shift amount|Φ_(a)-Φ_(t)| of the phases Φ_(a) and Φ_(t) of X-rays transmittedthrough an absorber and SrO improves most, i.e., |Φ_(a)-Φ_(t)|≦π±0.07 π,π±0.04 π, and π±0.22 π for Ni, Cu, and Au absorbers, respectively.

Similarly, FIGS. 20 to 22 show the phase shift characteristics whenabsorbers Au, Cu, and Ni are combined with the above transparent filmmaterials.

When Si₃N₄, SiC, Si, and C (diamond) are used as transparent films,these materials are the same as the membrane materials, so the phaseshift mask can be fabricated by forming the patterns directly onto amembrane by etching and filling an absorber. This makes it possible toreduce absorption by the membrane and the transparent film and therebydecrease the film thickness and the number of steps. Accordingly, thesematerials are convenient and preferable.

(Eight Embodiment)

In this embodiment, a method of manufacturing an X-ray maskcharacterized in that the absorber is filled in suitable transparentfilm patterns as shown in FIGS. 12A to 14B and suitable absorber andtransparent film materials will be described in detail.

When synchrotron radiation having an exposure wavelength region of 0.6to 1 nm is used, a Cu absorber and SiO₂ transparent film found to be asuitable absorber and transparent film material for phase shift controlare selected. By setting the depth of trenches in the SiO₂ transparentfilm pattern to be the film thickness for a desired phase shift amount,an SiO₂ film is formed on a membrane material and etched. Finally, theabsorber material is filled in the trenches to form the X-ray mask shownin FIG. 12A. When the Cu absorber and the SiO₂ film are combined, thefilm thickness for π phase shift is approximately 0.84 μm. Since theside walls of the obtained SiO₂ patterns can be made vertical, thismaterial is suited to filling an absorber material which requires thepattern structures with a high aspect ratio.

Hence, patterns with any shapes can be formed, so this mask structure issuitable not only for phase shift control but also for the fabricationof an absorber pattern with a high aspect ratio structure. The shiftamount |Φ_(a)-Φ_(t)| of the phases Φ_(a) and Φ_(t) of X-rays transmittedthrough the absorber and SiO₂ is |Φ_(a)-Φ_(t)|≦π±0.09 π. That is, thephase shift amount greatly improves compared to |Φ₁-Φ₂|≦π±0.125 π when πphase shift is performed by the conventional masks with no SiO₂transparent film pattern.

This mask is manufactured by using reflow sputtering as the filltechnique. A Cu absorber as a filling material is formed on SiO₂patterns by sputtering. The wafer is heated to allow the fillingmaterial to flow into trenches (holes) of the patterns, therebyaccurately burying the absorber into SiO₂ patterns. It is difficult bythe conventional vacuum vapor deposition or sputtering method with nothermal treatment to completely fill an absorber material in finetrenches of SiO₂ patterns with a high aspect ratio or completely coverthe bottom and side walls. This makes the formation of desired absorberpatterns extremely difficult. In this embodiment, micro-patterning iseasy because the reflow sputtering method is used as the fillingtechnique. It is possible by repeating reflow sputtering a plurality oftimes to completely fill the fine trenches of the SiO₂ patterns with Cuabsorber material and thereby accurately form fine patterns.

Reflow heating in the reflow sputtering method also has a film annealingeffect which decreases the stresses of the absorber and the SiO₂ film.Consequently, it is possible to control the stress distribution andimprove the image placement accuracy and CD (Critical Dimension)accuracy. In this embodiment, sputtering is used to deposit the absorberfilm on the transparent film patterns. However, chemical vapor phasedeposition can also be used to improve the film characteristic (stepcoverage) in the pattern trenches. Chemical vapor phase deposition isparticularly effective for a structure with a high aspect ratio.

The SiO₂ film was used as the transparent film. However, an SiON film issuitable for a transparent film material because stress control is easyin film formation. SiON exhibits no heat diffusion of Cu into the SiONfilm in 1-hour annealing at 500° C. according to various measurements(Auger electron spectroscopy or Rutherford backscattering spectroscopy).The SiON film is suitable as a transparent pattern layer for Cu absorberbecause the fill process can be done at high temperature without heatdiffusion of Cu. Therefore, highly accurate absorber patterns with novoids can be formed for the fabrication of Cu/SiON mask.

As the absorber material, it is desirable to use elements Mn, Co, Ni,Cu, Zn, Ga, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Yb, and Au havingrelatively low melting points (≦1,500° C.) in order to lower the reflowtemperature.

As the transparent film material, on the other hand, it is desirable touse materials with high-melting point, e.g., diamond, MgO, Al₂O ₃, SiO₂,Si₃N₄, SiC, CaO, Ti, TiO₂, SrO, SrS, Y₂O₃, YSi, Zr, and ZrO₂, havingrelatively high melting points 1,500° C.) and capable of withstandingthe reflow temperature. In X-ray exposure using synchrotron radiationhaving a wavelength of 0.6 to 1 nm, therefore, the use of SiO₂, SrO,SiC, Si₃N₄, or diamond as the transparent film material is desirablewhen the transmittances in this wavelength region described in the sixthembodiment are also taken into consideration.

A material (e.g., SiON) made of elements constituting the abovematerials is also apparently a suitable transparent film material.

Table 25 below shows the phase shift characteristics when elementshaving relatively low melting points and their alloys are filled asabsorber materials in SiO₂ transparent film patterns.

TABLE 25 Phase shift con- π phase shift trollability φ [π] Mask MaskMask Mask average film Phase shift deviation contrast contrast contrastcontrast thickness [nm] Δφ [π] Si₃N₄ 1 μm SiC 1 μm C 1 μm Si 1 μm Fillstructures in SiO₂ and SrO transparent films Co—SiO₂ 810.59 0.85 ≦ φ ≦1.14 6.95 7.05 6.54 7.14 Δφ = ±0.15 (2.73) (2.75) (2.65) (2.77) Co—SrO937.09 0.91 ≦ φ ≦ 1.09 6.96 7.06 6.50 7.15 Δφ = ±0.09 (2.42) (2.44)(2.36) (2.45) Ni—SiO₂ 776.97 0.88 ≦ φ ≦ 1.13 8.73 8.87 8.15 8.99 Δφ =±0.13 (3.22) (3.25) (3.12) (3.28) Ni—SrO 886.06 0.93 ≦ φ ≦ 1.07 8.869.00 8.21 9.12 Δφ = ±0.07 (2.86) (2.89) (2.77) (2.91) Cu—SiO₂ 843.010.91 ≦ φ ≦ 1.09 12.40 12.62 11.43 12.81 Δφ = ±0.09 (3.55) (3.58) (3.42)(3.61) Cu—SrO 968.98 0.96 ≦ φ ≦ 1.04 13.07 13.30 11.94 13.51 Δφ = ±0.04(3.15) (3.18) (3.04) (3.20) Zn—SiO₂ 1236.97 0.93 ≦ φ ≦ 1.07 23.11 23.6020.74 24.03 Δφ = ±0.07 (3.04) (3.07) (2.95) (3.09) Ag—SiO₂ 754.03 0.81 ≦φ ≦ 1.19 5.46 5.52 5.18 5.58 Δφ = ±0.19 (2.54) (2.56) (2.48) (2.58)Au—SiO₂ 556.44 0.75 ≦ φ ≦ 1.24 6.72 6.81 6.40 6.88 Δφ = ±0.25 (4.03)(4.07) (3.90) (4.10) Au—SrO 611.47 0.78 ≦ φ ≦ 1.22 6.70 6.78 6.36 6.85Δφ = ±0.22 (3.58) (3.61) (3.46) (3.63) Fill structures of alloys orstacked films in SiO₂ transmitting film Ce₁₃Au₇—SiO₂ 966.67 0.88 ≦ φ ≦1.12 25.74 26.25 23.35 26.69 Δφ = ±0.12 (4.17) (4.21) (4.03) (4.25)Pr₃Au₂—SiO₂ 981.88 0.90 ≦ φ ≦ 1.10 27.69 28.22 25.10 28.67 Δφ = ±0.10(4.15) (4.18) (4.01) (4.21) NdCo₉—SiO₂ 926.91 0.89 ≦ φ ≦ 1.11 11.0611.24 10.25 11.39 Δφ = ±0.11 (2.98) (3.00) (2.89) (3.02) NdNi₁₉—SiO₂832.86 0.89 ≦ φ ≦ 1.11 10.77 10.95 9.99 11.11 Δφ = ±0.11 (3.33) (3.36)(3.22) (3.38) NdCu₉—SiO₂ 949.29 0.93 ≦ φ ≦ 1.06 18.09 18.43 16.48 18.14Δφ = ±0.07 (3.67) (3.70) (3.54) (3.73) Nd₁₁Ir₉—SiO₂ 836.11 0.88 ≦ φ ≦1.12 28.11 28.59 25.91 29.00 Δφ = ±0.12 (5.23) (5.28) (5.06) (5.32)NdPt—SiO₂ 808.62 0.88 ≦ φ ≦ 1.12 23.49 23.90 21.49 24.26 Δφ = ±0.12(5.06) (5.11) (4.87) (5.15) Nd₂Au₃—SiO₂ 833.87 0.85 ≦ φ ≦ 1.13 21.3621.73 19.60 22.05 Δφ = ±0.13 (4.60) (4.64) (4.44) (4.68) Pm₃Au₂—SiO₂969.40 0.95 ≦ φ ≦ 1.05 38.18 38.95 34.32 39.63 Δφ = ±0.05 (4.87) (4.92)(4.69) (4.95) Sm₁₁Au₉—SiO₂ 960.16 0.96 ≦ φ ≦ 1.05 48.38 49.37 43.3550.24 Δφ = ±0.05 (5.46) (5.51) (5.25) (5.55) SmAu—SiO₂ 906.98 0.94 ≦ φ ≦1.06 39.06 39.82 35.27 40.49 Δφ = ±0.06 (5.43) (5.48) (5.22) (5.52)

The phase shift characteristic of the mask with any element or alloygreatly improves as compared with that of the conventional masks with notransparent film pattern.

From the foregoing, the X-ray mask of this embodiment characterized inthat the absorber shown in FIGS. 12A to 14B is embedded in thetransparent film patterns has the following advantages.

1) The X-ray mask using the absorber and the transparent film materialfound to be a suitable combination in the fifth embodiment is a goodphase shift mask in X-ray exposure using synchrotron radiation having awavelength region of 0.6 to 1 nm.

2) An SiO₂ transparent film has high X-ray transmittance and allows easyetching. Since the side walls of the obtained SiO₂ patterns can be madevertical, this material is suited to being filled with an absorbermaterial accurately.

3) In the reflow sputtering method, an absorber material flows intotrenches (holes) of patterns by heating. Therefore, the absorbermaterial is completely buried in fine trenches of transparent filmpatterns with a high aspect ratio, so mask patterns can be formed withhigh accuracy.

4) The reflow heating reduces stresses of the absorber and transparentfilm, and this reduces the errors caused by the film stress.

5) Since the absorber and transparent film are planarized to the flatsurface by polishing, foreign materials such as dust attaching to theX-ray mask can be removed by only cleaning the surface.

In this embodiment as described above, not only any desired phase shiftamount but also any mask contrast can be accurately controlled.Accordingly, the X-ray mask of this embodiment characterized in thatthese absorber materials are buried in transparent film patternssuppresses deterioration of the resolution resulting from diffraction bythe phase shift effect in a proximity X-ray lithography usingsynchrotron radiation. The process for making the X-ray mask with atransparent film pattern also decreases the stress of the films andthereby improves the image placement accuracy and CD (CriticalDimension) accuracy. Hence, this X-ray mask is suitably applicable tothe technology of forming very fine patterns of 0.2 μm or less.

In this embodiment, the characteristics of the absorber materials withexcellent phase shift controllability and the conventional absorbermaterials are compared with each other when these materials are used intransfer of various patterns (hole, island, line, space, andline-and-space) each having a size of 0.1 μm. Masks have structures asshown in FIG. 1 and FIGS. 12A to 14B, synchrotron radiation has anintensity in the wavelength region of 0.6 to 1 nm shown in FIG. 2, andthe gap size between the wafer and mask is 5 to 10 μm. Under theseconditions, proximity exposure is performed. The following absorberswere used, and results were compared with each other:

1) A structure in which an SiO₂ film pattern is filled with Cu (copper:atomic number 29)

π phase shift absorber film thickness: d_(a)=843.01 nm

phase shift controllability: |Φ_(a)-Φ_(t)|≦π±0.09 π

2) Ta (tantalum: atomic number 73)

π phase shift absorber film thickness: d_(a)=679.50 nm

phase shift controllability: |Φ₁-Φ₂|≦π±0.54π

At this time, the dose (or the logarithm of the light intensity) at eachposition on a wafer as a function of gap size between the mask and waferis obtained (normally, this chart is called an Exposure-Gap Trees) toevaluate an exposure latitude. The exposure latitude is defined as aregion between doses of exposure light beams required to obtain patternshaving relative differences within ±10% from the pattern size in the gapsize between a given mask and wafer (in this case, a region between thedose for a size of 90 nm and the dose for a size of 110 nm, providedthat the pattern size is 100 nm). The exposure latitude was obtained asa function of gap size in the range of 5 to 10 μm. An overlap region ofthe exposure latitudes for all the patterns, i.e., a hole, island, line,space, and line-and-space is defined as an exposure window. The largerthe exposure latitude and exposure window are, the larger the processlatitude and process margin are. The resultant mask with large exposurewindow can be regarded as an excellent X-ray mask capable oftransferring high-resolution patterns.

The Cu-SiO₂ and Ta absorber film thicknesses were changed to evaluatetheir exposure characteristics. The exposure latitude and exposurewindow of the Cu-SiO₂ X-ray mask having a film thickness of about 550 nmwere maximum, and the exposure latitude and exposure window of the TaX-ray mask having a film thickness of about 400 nm were maximum. Atthese optimal film thicknesses, the exposure characteristics of theCu-SiO₂ X-ray mask are better than those of the Ta X-ray mask. At anygap size in the range of 5 to 10 μm, the exposure latitude and exposurewindow of the Cu-SiO₂ absorber mask are larger than those of the Taabsorber mask. The exposure latitude of the line-and-space of theCu-SiO₂ mask at a gap size of 10 μm and the exposure window of theCu-SiO₂ mask at a gap size of 5 μm are larger than those of the Ta maskby about 1.3 times and about 14.4 times, respectively.

These results are apparently derived from the phase shiftcontrollability because the absorption characteristics of the Cu-SiO₂and Ta absorbers are almost identical (the contrast values of theCu-SiO₂ and Ta masks each having the absorber film thickness of 400 nmare 3.42 to 3.61 and 3.43 to 3.58, respectively; see Table 6).

In a proximity X-ray lithography, since the gap size between the maskand wafer is larger than the pattern size, the influence of diffractionand the geometric optical path length difference occurs. The π phaseshift amount by the absorber may not always be optimal. However, sincethe phase shift deviation ratio in the wavelength region does not changeregardless of a change in film thickness, phase shift controllability ofthe mask is important.

Cu-SiO₂ is a good absorber material meeting all of the following threeconditions:

1) ΔΦ≦0.10 π (0.95≦|cosΦ|≦1)

The maximum and minimum phase shift amounts with respect to thewavelengths in the exposure wavelength region are ±10% or less of theaverage phase shift amount in the exposure wavelength region.

2) The mask contrast value C for the π phase shift film thickness is10<C<20.

3) π phase shift film thickness d_(a)≦1,000 nm (the aspect ratio is 10or less in patterns having an L/S width of 0.1 μm).

In a method of performing exposure by using an X-ray mask using any ofthese materials as an absorber, the mask contrast is appropriate, andthe phase shift amounts of X-ray beams transmitted through the absorberis substantially constant over the whole exposure wavelength band. So,the phase shift amount of the transmitted X-ray beams is controlled toachieve the phase shift effect. Since this greatly improves theresolution of pattern-transfer, the method is suited to transfer of finepatterns. In this embodiment, the results obtained when the phase shiftamount is π are described. However, in the case of a halftone mask suchas an X-ray mask, conditions by which the phase shift amount is π arenot necessarily optimum, but the relationship between the absorptioncharacteristic (mask contrast) and the phase shift characteristic isimportant. Therefore, a preferable mask contrast value and phase shiftamount change in accordance with experimental conditions, e.g., patternsto be transferred, the gap size between the mask and the wafer, and theresist material. However, it is obvious that by the use of the absorbermaterials and the combinations of the absorber materials and transparentfilm materials meeting the aforementioned conditions explained in thethird to seventh embodiments, it is easy to form an X-ray mask (phaseshift mask) having a desired mask contrast value and phase shift amount.Also, even when the materials shown in Tables 12, 13, and 25 and theabovementioned composition ratios are not used, materials meeting thethree conditions described above exist in binary compounds formed bycombining Groups III and IV or Groups I and IV.

A desired phase shift amount and mask contrast can be obtained with highaccuracy by using, as an absorber, any of Co (cobalt), Ni (nickel), Cu(copper), Zn (zinc), Ga (gallium), lanthanoid rare-earth elements(atomic numbers 57 to 71), e.g., La (lanthanum), Ce (cerium), Pr(praseodymium), Nd (neodymium), Pm (promethium), Sm (samarium), Eu(europium), Gd (gadolinium), Tb (terbium), Dy (dysprosium), Ho(holmium), Er (Erbium), Tm (thulium), Yb (ytterbium), Lu (lutetium), andtheir alloys, or an alloy of any of Cr (chromium), Mn (manganese), Fe(iron), Hf (hafnium), Ta (tantalum), W (tungsten), Re (rhenium), Os(osmium), Ir (iridium), Pt (platinum), Au (gold), and Hg (mercury) andany of lanthanoid rare-earth elements (atomic numbers 57 to 71).

(Ninth Embodiment)

In the eighth embodiment, a method of forming an X-ray absorber buriedinto a transparent film pattern when a material having a lower meltingpoint than that of a transparent film material is chosen as an absorbermaterial is described. In this embodiment, a method of forming an X-rayabsorber and a transparent film when a material having a higher meltingpoint than that of a transparent film material is chosen as an absorbermaterial will be described.

After absorber patterns are formed, a transparent film is deposited onthe absorber patterns and buried in absorber pattern trenches. Thisdeposition/film formation step is performed by sputtering or chemicalvapor phase deposition. The transparent film is buried in the absorptionpattern trenches by a heating step following the deposition/filmformation step.

In this embodiment, Sr and Au are used as a transparent film materialand an absorber material, respectively, in X-ray exposure usingsynchrotron radiation having a wavelength region of 0.6 to 1 nm. Sincethe melting points of Sr and Au are 770° C. and 1,064° C., respectively,the structure shown in FIGS. 12A to 14B in which the transparent film isburied in the absorber pattern trenches can be formed by a reflow step.Equation (9′) presented earlier shows that Sr has a phase compensatingeffect for Au absorber (Table 16). In effect, the phase shift deviationcan be improved from ΔΦ_(D)=0.25 π to ΔΦ_(D)=0.225 π by the Srtransparent film. Analogously, even when Pt is used as the absorbermaterial, the phase shift deviation can be improved from ΔΦ_(D)=0.27 πto ΔΦ_(D)=0.25 π by the Sr transparent film.

From the foregoing, the transparent film material used in thisembodiment is desirably a material having a lower melting point thanthat of the absorber material. This material is an element having allabsorption edges in a wavelength region shorter than the shortestwavelength or longer than the longest wavelength of the exposurewavelength region, or an element having an absorption edge near theshortest wavelength (within 0.1 nm), or a compound or multi-layer filmof the element. The material desirably has small absorption and hightransmittance with respect to the exposure wavelength.

The transparent materials meeting the above conditions in exposure usingsynchrotron radiation having a maximum light intensity wavelength of 0.6to 1 nm are Ca, Sr, and Ba having melting points of 1,000° C. or lessand their compounds.

The absorber material is a material having a melting point higher thanthat of the transparent film material. This material is an elementhaving all absorption edges in a wavelength region shorter than theshortest wavelength or longer than the longest wavelength of theexposure wavelength region, or a compound or multi-layer film of theelement. The material desirably has large absorption of the exposurewavelength.

The absorber materials meeting the above conditions in exposure usingsynchrotron radiation having a maximum light intensity wavelength of 0.6to 1 nm are Os, Ir, and Pt having melting points of 1,500° C. or moreand their alloys.

(10th Embodiment)

This embodiment shows an exposure wavelength region for various elementsand compounds to obtain high phase shift controllability used asabsorbers when a wide-band exposure light source such as synchrotronradiation is used. When an exposure light source having a wavelengthdistribution in an exposure wavelength region suitable for an absorbermaterial is used, the phase shift amount is constant over the entireexposure light wavelength region, and the phase shift effect improvesthe resolution of pattern transfer.

An exposure wavelength region is defined as a wavelength region havingan intensity {fraction (1/10)} the light intensity at the wavelength ofthe maximum light intensity incident on the X-ray mask or more. Tables26 and 27 below show elements and compounds meeting

1) |ΔΦ|≦0.10 π (0.95≦|cosΦ|≦1)

where Φ: the maximum deviation from the phase shift π in the exposurewavelength region when the absorber film thickness is the π phase shiftaverage film thickness. Accordingly, 1) means that the maximum andminimum phase shift amounts in the exposure wavelength region are ±10%or less of the average phase shift amount in this exposure wavelengthregion.

2) Δλ=longest wavelength in exposure wavelength region—shortestwavelength in exposure wavelength region≧0.4 nm

3) The shortest wavelength in the exposure wavelength region is 1.5 nmor less in the π phase shift mask shown in FIG. 1.

TABLE 26 Exposure wavelength region of |Δφ| ≦ 0.10π [Å] Absorptioncoefficient α at center wavelength [cm⁻¹] π phase average film thicknessd [nm] $\frac{1}{\exp \left( {{- \alpha} \times d} \right)}$

i) Shortest wavelength 4-6 Å 31 Ga 5.98 ≦ λ ≦ 10.4 2.9 × 10⁴ @ 8.19 Å1080.6 26.7 32 Ge 5.58 ≦ λ ≦ 9.59 2.5 × 10⁴ @ 7.59 Å 1286.6 23.7 60 Nd5.37 ≦ λ ≦ 11.8 3.9 × 10⁴ @ 8.59 Å 1189.1 103 61 Pm 5.40 ≦ λ ≦ 10.9 4.0× 10⁴ @ 8.17 Å 1134.2 86.3 62 Sm 5.08 ≦ λ ≦ 10.2 4.0 × 10⁴ @ 7.64 Å1046.5 64.4 63 Eu 5.46 ≦ λ ≦ 9.96 2.6 × 10⁴ @ 7.71 Å 1567.4 60.7 64 Gd4.80 ≦ λ ≦ 9.56 3.9 × 10⁴ @ 7.10 Å 1205.2 111 65 Td 4.79 ≦ λ ≦ 9.39 3.7× 10⁴ @ 7.09 Å 1140.3 66.4 66 Dy 4.67 ≦ λ ≦ 9.01 3.5 × 10⁴ @ 6.84 Å1141.7 54.4 67 Ho 4.35 ≦ λ ≦ 8.58 3.6 × 10⁴ @ 6.47 Å 1179.6 71.5 ii)Shortest wavelength 6-8 Å 28 Ni 7.64 ≦ λ ≦ 13.4 6.7 × 10⁴ @ 10.5 Å 535.0 36.0 29 Cu 6.95 ≦ λ ≦ 12.6 6.0 × 10⁴ @ 9.75 Å  602.8 37.4 30 Zn6.49 ≦ λ ≦ 11.3 4.2 × 10⁴ @ 8.90 Å  800.7 28.9 57 La 6.27 ≦ λ ≦ 13.8 4.1× 10⁴ @ 10.0 Å 1214.6 139 58 Ce 6.70 ≦ λ ≦ 12.3 4.9 × 10⁴ @ 9.50 Å 986.4 120 59 Pr 6.06 ≦ λ ≦ 12.0 3.7 × 10⁴ @ 9.05 Å 1151.7 68.5 iii)Shortest wavelength 8-10 Å 25 Mn 9.76 ≦ λ ≦ 17.5 7.4 × 10⁴ @ 13.6 Å 527.2 50.0 26 Fe 8.97 ≦ λ ≦ 16.0 7.2 × 10⁴ @ 12.5 Å  528.9 44.7 27 Co8.26 ≦ λ ≦ 14.6 7.0 × 10⁴ @ 11.4 Å  525.4 39.3 49 In 9.56 ≦ λ ≦ 18.0 7.1× 10⁴ @ 13.8 Å  657.1 109 50 Sn 9.24 ≦ λ ≦ 16.6 6.8 × 10⁴ @ 12.9 Å 682.9 103 51 Sb 9.15 ≦ λ ≦ 20.5 7.5 × 10⁴ @ 14.8 Å  750.5 278 52 Te8.50 ≦ λ ≦ 18.8 6.4 × 10⁴ @ 13.6 Å  888.6 290 53 I 8.15 ≦ λ ≦ 17.7 4.9 ×10⁴ @ 12.9 Å 1143.3 284 55 Cs 8.44 ≦ λ ≦ 14.1 2.0 × 10⁴ @ 11.3 Å 2846.0272

TABLE 27 Exposure wavelength region of |Δφ| ≦ 0.10π [Å] Absorptioncoefficient α at center wavelength [cm⁻¹] π phase average film thicknessd [nm] $\frac{1}{\exp \left( {{- \alpha} \times d} \right)}$

i) Shortest wavelength 10-12 Å 23 V 11.7 ≦ λ ≦ 20.9 7.2 × 10⁴ @ 16.3 Å563.6 56.6 24 Cr 10.5 ≦ λ ≦ 19.2 8.5 × 10⁴ @ 14.9 Å 492.7 64.3 46 Pd11.0 ≦ λ ≦ 23.0 1.6 × 10⁵ @ 17.0 Å 343.7 206 47 Ag 10.1 ≦ λ ≦ 22.2 1.3 ×10⁵ @ 16.1 Å 381.4 166 48 Cd 11.3 ≦ λ ≦ 20.5 1.1 × 10⁵ @ 15.9 Å 526.5265 76 Os 11.6 ≦ λ ≦ 15.6 1.1 × 10⁵ @ 13.6 Å 251.5 15.9 77 Ir 11.2 ≦ λ ≦15.2 1.1 × 10⁵ @ 13.2 Å 257.8 17.0 78 Pt 11.1 ≦ λ ≦ 15.2 1.3 × 10⁵ @13.1 Å 244.4 14.7 79 Au 10.3 ≦ λ ≦ 14.3 9.6 × 10⁴ @ 12.3 Å 313.6 31.511.0 ≦ λ ≦ 55.7 2.6 × 10⁵ @ 33.4 Å 299.4 2231 v) Shortest wavelength12-15 Å 22 Ti 12.8 ≦ λ ≦ 23.8 6.6 × 10⁴ @ 18.3 Å 659.3 75.3 40 Zr 14.9 ≦λ ≦ 36.0 1.2 × 10⁵ @ 25.5 Å 479.9 295 41 Nb 14.7 ≦ λ ≦ 35.1 1.5 × 10⁵ @24.9 Å 379.4 275 42 Mo 13.4 ≦ λ ≦ 34.3 1.7 × 10⁵ @ 23.9 Å 341.7 344 43Tc 13.7 ≦ λ ≦ 27.5 1.8 × 10⁵ @ 20.6 Å 301.0 206 44 Ru 12.6 ≦ λ ≦ 25.11.8 × 10⁵ @ 18.9 Å 303.7 159 45 Rh 12.0 ≦ λ ≦ 24.2 1.7 × 10⁵ @ 18.1 Å307.9 188 67 Ho 15.0 ≦ λ ≦ 19.0 4.4 × 10⁴ @ 17.0 Å 590.9 13.2 68 Er 14.7≦ λ ≦ 18.7 4.7 × 10⁴ @ 16.7 Å 548.6 12.9 69 Tm 14.2 ≦ λ ≦ 18.2 3.9 × 10⁴@ 16.2 Å 547.5 8.28 70 Yb 13.8 ≦ λ ≦ 17.8 3.6 × 10⁴ @ 15.8 Å 735.9 14.671 Lu 13.6 ≦ λ ≦ 17.6 5.2 × 10⁴ @ 15.6 Å 517.3 14.6 (24.7 ≦ λ ≦ 73.7)(1.9 × 10⁵ @ 49.2 Å) (366.6) (915) 72 Hf 13.3 ≦ λ ≦ 17.4 7.1 × 10⁴ @15.4 Å 395.1 16.6 (23.0 ≦ λ ≦ 72.7) (2.5 × 10⁵ @ 49.2 Å) (292.1) (1572)73 Ta 12.7 ≦ λ ≦ 16.7 8.6 × 10⁴ @ 14.7 Å 320.0 15.7 14.5 ≦ λ ≦ 20.3 1.2× 10⁵ @ 17.4 Å 289.4 34.1 (19.3 ≦ λ ≦ 70.8) (3.1 × 10⁵ @ 45.1 Å) (242.1)(1610) Ta₄B 12.8 ≦ λ ≦ 16.9 7.1 × 10⁴ @ 14.9 Å 377.1 14.4 15.0 ≦ λ ≦23.4 1.2 × 10⁴ @ 19.2 Å 327.3 43.1 (22.2 ≦ λ ≦ 73.7) (2.7 × 10⁴ @ 48.0Å) (280.6) (1696) Ta₄Ge 13.5 ≦ λ ≦ 17.7 7.8 × 10⁴ @ 15.6 Å 343.8 14.715.0 ≦ λ ≦ 22.5 1.1 × 10⁵ @ 18.8 Å 316.3 32.4 (22.5 ≦ λ ≦ 80.7) (3.0 ×10⁵ @ 51.6 Å) (253.4) (1999) 74 W 12.5 ≦ λ ≦ 16.5 8.6 × 10⁴ @ 14.7 Å277.3 16.0 14.5 ≦ λ ≦ 21.8 1.5 × 10⁵ @ 18.1 Å 246.1 40.1 (19.3 ≦ λ ≦69.2) (3.5 × 10⁵ @ 43.0 Å) (225.4) (2385) 75 Re 12.1 ≦ λ ≦ 16.3 1.1 ×10⁵ @ 14.2 Å 255.5 16.6 (15.2 ≦ λ ≦ 58.9) (3.4 × 10⁵ @ 37.0 Å) (218.2)(1492) 76 Os 14.9 ≦ λ ≦ 59.8 3.5 × 10⁵ @ 37.4 Å 210.2 1504 77 Ir 13.4 ≦λ ≦ 74.0 3.8 × 10⁵ @ 43.7 Å 225.8 5454 78 Pt 12.8 ≦ λ ≦ 53.7 3.3 × 10⁵ @33.3 Å 244.4 2989

These elements and compounds are classified into the following fivegroups in accordance with the shortest wavelengths in the exposurewavelength region:

i) shortest wavelength 0.4 to 0.6 nm

ii) shortest wavelength 0.6 to 0.8 nm

iii) shortest wavelength 0.8 to 1.0 nm

iv) shortest wavelength 1.0 to 1.2 nm

v) shortest wavelength 1.2 to 1.5 nm

Tables 26 and 27 also show an absorption coefficient α at the centerwavelength in the exposure wavelength region, a π phase shift averagefilm thickness d, and 1/exp(−α×d). The mask contrast value changes withthe intensity profile of synchrotron radiation. 1/exp(−α×d) is anapproximate value of the mask contrast when an exposure wavelengthregion meeting |ΔΦ|≦0.10 π is used.

Each of the elements and compounds listed in Tables 26 and 27 has alarge value of 1/exp(−α×d). So, it is obvious that any of these elementsand compounds is an absorber material having good phase shift andabsorption characteristics when synchrotron radiation having awavelength distribution in the wavelength region shown in these tablesis used. Accordingly, it is important to select the material of anabsorber in accordance with the exposure wavelength region ofsynchrotron radiation shown in Tables 26 and 27.

Also, elements from Lu to Au having atomic numbers 71 to 79 can satisfy|ΔΦ|≦0.10 π (0.95≦|cosΦ|≦1) for an exposure wavelength region Δλ of 0.4nm or more in the wide wavelength region of

Lu: 1.36 nm≦λ≦7.37 nn

Ta: 1.27 nm≦λ≦7.08 nm

Ta₄B: 1.27 nm≦λ≦7.08 nm

Ta₄Ge: 1.35 nm≦λ≦8.07 nm

W: 1.25 nm≦λ≦6.92 nm

Re: 1.21 nm≦λ≦5.89 nm

Os: 1.49 nm≦λ≦5.98 nm

Ir: 1.34 nm≦λ≦7.40 nm

Pt: 1.28 nm≦λ≦5.37 nm

Au: 1.03 nm≦λ≦5.57 nm

In the wavelength region of 1 nm or more, each element or compound haslarge absorption and obtains the π phase shift with small filmthickness. Therefore, these elements and compounds are suitable absorbermaterials in this exposure wavelength region.

(11th Embodiment)

An embodiment of an exposure apparatus for manufacturing a microdevice(e.g., a semiconductor device, thin film magnetic head, or micromachine)using the mask explained above will be described below.

FIG. 23 is a view showing the arrangement of an X-ray exposure apparatusof this embodiment. A condenser mirror 22 condenses light radiated froma synchrotron radiation source 14 to increase the X-ray intensity. Arocking mirror 23 shapes the condensed light into parallel light andscans an exposure region, thereby widening the exposure area. In anexposure method in which an X-ray mirror reflects synchrotron radiation,a large difference is produced between wavelength distributions inaccordance with the exposure positions. However, in the X-ray mask ofthis embodiment, the phase shift amount has no wavelength dependence.Accordingly, exposure variations and resolution deterioration can besuppressed.

The apparatus includes three X-ray extracting windows, i.e., a diamondwindow 24, a beryllium window 25, and a silicon nitride window 26 whichisolate ultra-high vacuum A/high vacuum B, high vacuum B/atmospherichelium C, and helium C/air D, respectively. An X-ray mask 27 has thestructure explained in any of the abovementioned embodiments. Theconditions described in these embodiments are set such that the maximumintensity wavelength of exposure light transmitted through the membraneis 0.6 to 1 nm. Patterns formed on the X-ray mask 27 are transferred byexposure onto a wafer 29 held on a wafer stage 28 by step-and-repeat orscanning.

(12th Embodiment)

A method of manufacturing an X-ray mask of the present invention will bedescribed below.

FIGS. 24A to 24D and FIGS. 25A to 25D are cross-sectional views showingthe steps of manufacturing an X-ray mask according to the 12thembodiment of the present invention.

First, as shown in FIG. 24A, a 2-μm thick SiC film serving as a thinX-ray transparent film 102 is formed on a cleaned 525-μm thick 4-inch Si(100) wafer 101 at a substrate temperature of 1,250° C. and a pressureof 30 Torr by using low-pressure CVD by supplying 150 sccm of 10%hydrogen-diluted silane gas, 65 sccm of 10% hydrogen diluted acetylenegas, and 150 sccm of 100% hydrogen chloride gas, together with 10 SLM ofhydrogen as a carrier gas, into a reaction tube. Subsequently, a 98-nmthick alumina film serving as an antireflection film/etching stopper 108is formed on the substrate surface at an Ar pressure of 1 mTorr by usingan RF sputtering apparatus. On this antireflection film/etching stopper103, a 0.8-μm thick SiO₂ film serving as a patterning layer 104 isformed by CVD using TEOS as a main raw material. After the filmformation, annealing is performed to adjust the stress of this SiO₂ filmto substantially 0 MPa.

Next, as shown in FIG. 24B, an SiC film in a region having a radius of70 mm in a central portion of the back surface is removed by supplying25 sccm of CF₄ gas and 40 sccm of O₂ gas at a pressure of 10 mTorr andan RF power of 200 W by using an RIE apparatus and an aluminum etchingmask (not shown), thereby forming an opening 105 as a mask of backetching.

As shown in FIG. 24C, an ultraviolet-curing epoxy resin adhesive (notshown) is used to adhere a glass ring 125 mm in outer diameter, 72 mm ininner diameter, and 6.2 mm in thickness as a frame 106 to form thesubstrate. Additionally, a back etching apparatus is used to drop a 1:1solution mixture of hydrofluoric acid and nitric acid onto the portionfrom which SiC is removed, thereby etching away the Si wafer 101 fromthat portion.

As shown in FIG. 24D, a commercially available electron beam positiveresist ZEP-520 (viscosity 12 cps) is spin-coated on the SiO₂ film at arotating speed of 2,000 rpm for 50 sec to form a 0.3-μm thickphotosensitive film 107. This resist is baked at 175° C. for 2 min byusing a hot plate. An electron beam lithography apparatus whoseacceleration voltage is 75 kV is used to form patterns on thephotosensitive film 107. To obtain desired highly accurate pattern,multiple electron beam writing technique by which patterns areoverwritten four times is performed. Also, proximity effect correctionby dose correction is performed with a reference dose of 96 μC/cm².

After the resist pattern is formed, it is developed at a liquidtemperature of 18° C. for 1 min by using a commercially availabledeveloper ZEP-RD. Subsequently, the developer is removed by rinsing for1 min by MIBK. With the formed resist patterns, CHF₃ and CO gases areused to etch the SiO₂ film 104 by reactive ion etching. After that, theresidual resist 107 is removed by ashing in oxygen plasma, and theresultant structure is cleaned in a solution mixture of sulfuric acidand hydrogen peroxide water.

Next, as shown in FIG. 25A, a 0.6-μm thick copper (Cu) film serving asan X-ray absorber 108 is formed at an Ar pressure of 3 mTorr by using anRF sputtering apparatus. As shown in FIG. 25B, annealing is performed inthe same vacuum chamber as sputtering at 550° C. for 1 min, therebyreflowing the X-ray absorber 108 in the patterns of the SiO₂ film 104.

Finally, excess Cu is removed by the following method called resist etchback. First, as shown in FIG. 25C, the same apparatus as used in theabove resist coating is used to form a film of the commerciallyavailable electron beam resist ZEP-520 (viscosity 12 cps) by spincoating at a rotating speed of 2,000 rpm for 50 sec. The film is thenbaked at 175° C. for 2 min by using a hot plate to form a 0.3-μm thickresist film 109. The surface of the coated film is substantially flatdue to the nature of spin coating.

As shown in FIG. 25D, the mask surface is etched by reactive ion etchingusing HBr gas until the SiO₂ surface is exposed with the condition thatthe etching rates of the resist film 109 and the Cu film 108 aresubstantially equal.

A desired X-ray mask can be fabricated by the above method, and the maskformed in this embodiment has the following advantages. First, theinternal stress of the absorber can be controlled to a desire value, soa high-accuracy X-ray mask can be easily obtained. The reason for thisis as follows.

In an X-ray absorber directly patterning by the conventional reactiveion etching, internal stress generated in the deposition process of theabsorber remains. To form a high-accuracy X-ray mask, therefore, it isnecessary to accurately control the film deposition conditions andsuppress the in-plane stress distribution to 5 Mpa or less, a very smallvalue. In this embodiment, however, annealing is performed after theformation of the absorber film to induce the reflow. Consequently, theinternal stress during the film formation is once fluidly released andhence depends only upon the reflow step. That is, if temperature controlin the reflow step is well controlled including the in-plane uniformity,an absorber with desired internal stress can be formed. Usually, stressadjustment by temperature control in the reflow step is far easier thanstress control in the sputtering step, so a stress distribution of about1 MPa can be obtained. Accordingly, a high-accuracy X-ray mask can beobtained by this embodiment.

Second, this embodiment uses apparatuses having the same coatingcharacteristics, preferably, the same apparatus in the first resistcoating step performed to form mask patterns and the second resistcoating step for the resist etch back. Therefore, the CD (CriticalDimension) accuracy can improve as will be described below.

As is generally known, as shown in FIG. 26A, if electron beam writingand development are performed when the resist film thickness has adistribution, the dimensions change in accordance with the resist filmthickness, i.e., the dimensions of a portion where the resist filmthickness is large become smaller than the dimensions of a portion wherethe resist film thickness is small even if the same pattern is writtenunder the same conditions. More specifically, a resist film thicknessvariation of 1% sometimes produces a dimensional variation of about 1%.However, when the resist etch back step is performed by using resistcoating apparatuses having the same coating characteristics as in thisembodiment, as shown in FIG. 26B, in a portion where the dimensionsdecrease due to a large resist film thickness in the electron beamlithography, the resist film thickness is large in the resist etch backstep. Therefore, after the completion of the resist etch back step, anabsorber in a portion where the pattern size of absorber decreases dueto the resist film thickness distribution, has a larger film thicknessthan that in a portion where the pattern size of absorber is large, asshown in FIG. 26C.

When this mask is used in actual exposure, the large film thicknessraises the contrast in a portion where the pattern size of absorber issmall, and the small film thickness lowers the contrast in a portionwhere the pattern size of absorber is large. These factors cancel eachother out and improve the dimensional uniformity of transferredpatterns, improving the CD (Critical Dimension) accuracy. That is, thisembodiment can alleviate deterioration of the CD accuracy by thedimensional distribution of pattern due to the resist film thicknessdistribution.

In this embodiment, another material film can be formed by spin coating,e.g., an SOG film or an ITO film. These material films can also be usedinstead of the resist film 109.

A mask fabricated by the above steps was used to transfer patterns ontoa resist film formed on an Si wafer by using a beam line with an SORlight source, mirrors, and a vacuum barrier Be film. The exposure lighthas a center wavelength of 0.8 nm. Consequently, the patterns with aline width of 70 nm were transferred with high resolution.

(13th Embodiment)

In the 12th embodiment, excess Cu remaining in a flat portion is removedby resist etch back. However, this excess Cu can also be removed bypolishing by using an apparatus with the following mechanism.Conventional polishing apparatuses can hardly polish an object, such asan X-ray mask, composed of a thin self-supporting film. This embodimentmakes this polishing possible by filling the non-polishing surface sideof a mask with a fluid and controlling the pressure of this fluid.

FIG. 27 is a sectional view showing a polishing apparatus according tothis embodiment. Similar to the general polishing apparatuses, apolishing pad 12 made of resin-impregnated non-woven fabric is attachedto the upper surface of a turntable 211. A polishing slurry 213 issupplied via a supply amount control mechanism 215 from a polishingslurry tank 214 and discharged near the polishing pad 212 through apolishing slurry supply pipe 216.

A mask 217 after the reflow treatment is fixed to a pedestal 219 via arubber O-ring 218 by a clamp 220. A supply pipe 222 and a discharge pipe223 of pure water as a pressure adjusting fluid 221 are connected to thepedestal 219. The whole pedestal is connected to a rotatable mechanism.A pressure gauge 224 is connected to the discharge pipe 223. Flow rateadjusting valves 225 a and 225 b are connected to the supply pipe 222and the discharge pipe 223, respectively. The flow rate is controlled inaccordance with an output from the pressure gauge 224, so the pressureof the fluid 221 in the pedestal is held constant. Since this fluidcirculates via a thermostat 226, the temperature of the surface of maskcan be kept constant during polishing. This stabilizes the processsensitive to temperature.

To further improve the accuracy, a sensor 227 is attached to thepedestal 219 to monitor the distance to the thin X-ray transparent filmof the mask. A computer 228 receives an output from this sensor 227.Accordingly, the pressure of the fluid 221 can be controlled by usingnot only the output from the pressure gauge 224 but also the output fromthe distance sensor 227, if necessary. Displacement of the X-ray masksurface is usually very sensitive to the pressure. Additionally, thepressure applied to the polished surface and the shape uniformity of thepolished surface are important in the polishing step. Therefore, the useof this sensor for monitoring the distance to the X-ray mask surfacegreatly helps stabilize the polishing step. Also, in addition to the twoflow rate adjusting valves, a variable volume mechanism 229 by acylinder is equipped to control the volume of the fluid between theseflow rate adjusting valves. This allows more precise pressure control.

More specifically, while the height of the X-ray mask surface is heldconstant at a fluid pressure of 300 g/cm², the turntable 211 and thepedestal 219 are rotated in opposite directions at a rotating speed of100 rpm, and the polishing slurry 213 is supplied to the polishing pad212 at a rate of 10 ml/min to remove excess Cu. The polishing slurry iscomposed of 5.3 wt % of silica grains with an average size of 30 nm aspolishing grains in a solution mixture of 0.12 mol/l of an aqueousglycine (C₂H₅O₂N) solution and 0.44 mol/l of hydrogen peroxide water(H₂O₂) with 0.001 mol/l of benzotriazole (C₆H₅N₃).

Under the above conditions, the Cu polishing rate is approximately 90nm/min, i.e., the processing can be performed at satisfactory rate. Theend point of the polishing step is detected by monitoring both of theprocessing time and the voltage change in the drive motor of theturntable. That is, the voltage of the drive motor of the turntableusually rises to a substantially constant voltage immediately after thebeginning of polishing and again rises when Cu residual in a wide flatportion is almost removed. Therefore, the processing can be performedwith high reproducibility by detecting this voltage rise and stoppingthe polishing step. The polished substrate is removed from the polishingapparatus and washed with pure water to remove the polishing slurrytherefrom. The resultant substrate is dipped in dissolved ozone waterwith an ozone concentration of 0.001% for 3 min and then in anaqueous-diluted hydrofluoric acid solution with a hydrofluoric acidconcentration of 5% for 1.5 min. to remove the residual organiccompounds. Finally, the substrate is washed with pure water. In thismanner, a series of processes are complete.

In this embodiment, it is important that the polishing apparatus cantreat the processes for an X-ray mask. So, other various methods can beused as for the polishing conditions such as the polishing pressure,rotating speeds of the turntable and pedestal, end point detection, andpolishing slurry. For example, the end point can also be detected bymonitoring the pH of the polishing slurry on the polishing pad or thetemperature of the polishing pad. As the polishing slurry, it ispossible to use alumina grains, titania grains, zirconia grains, ceriagrains, silicon carbide grains, diamond grains, or a mixture of thesegrains including silica grains, instead of silica grains. Furthermore,aminoacetic acid, aminosulfuric acid, or a mixture of these acids can beused instead of an aqueous glycine solution. It is also possible to usenitric acid, hypochlorous acid, ozone water, ammonium nitrate, ammoniumchloride, or chromic acid, instead of hydrogen peroxide water. Theaddition of benzotriazole is not always necessary, and the material tobe added is not necessarily benzotriazole. That is, this material needonly form a chelating compound or a complex compound together with thematerial to be polished. Therefore, it is possible to use abenzotriazole derivative, thio urea, a thiourea derivative,benzimidazole, triazole, ethylenediamine, cysteine, or a mixturecontaining these materials.

A mask manufactured by the above steps was used to transfer patternsonto a resist film on an Si wafer by using a beam line with an SOR lightsource, mirrors, and a vacuum barrier Be film and then exposure lighthas a center wavelength of 0.8 nm. Consequently, the patterns with aline width of 70 nm were transferred with high resolution.

With a shrink in the design rule, it becomes difficult to completelyfill the high aspect ratio trenches of patterns with absorber materialby one reflow step. If this is the case, it is only necessary to fillthese trenches by sputtering and reflow a plurality of times. Morespecifically, instead of forming a 0.6-μm thick Cu film at once, a0.2-μm thick Cu film as an absorber 8 is formed at an Ar pressure of 3mTorr by using, e.g., an RF sputtering apparatus. In the same vacuum asthis sputtering, annealing is performed at 550° C. for 1 min to reflowand fill the trenches of patterns. A series of these steps are repeatedthree times to reflow and fill the trenches. If necessary, resist etchback or polishing can be performed between each annealing step and thenext sputtering step to remove unnecessary Cu from the patterns of theSiO₂ film 4 previously.

In the above embodiment, Cu is used as an absorber. However, the presentinvention can also be applied when absorber materials other than Cu,e.g., W, Ta, Ru, Re, Au, Os, Zn, Pb, Pt, and their compounds are used.Some of these materials have high melting points and hence are difficultto reflow. However, this reflow step can be omitted because the stepitself is not essential to the present invention. Even if the reflowstep is omitted, a desired mask can be formed by performing the resistetch back step or the polishing step. The absorber film formation methodis also not limited to sputtering and can be done by any of variousmethods such as simple vapor deposition, electrolytic plating,electroless plating, thermal CVD, and plasma CVD. When electrolyticplating is used, it is preferable to replace the antireflectionfilm/etching stopper 103 with a conductive material such as a thin metalfilm of, e.g., Cr or Ni, or an ITO film.

In this embodiment, the patterning of the absorber of an X-ray mask withhigh aspect structures can be performed without using the RIE process.Accordingly, various materials can be readily used as the absorbermaterial of an X-ray mask even if they are unsuitable for the patterningby RIE.

According to the present invention as has been described in detailabove, it is possible to realize an X-ray mask which has remarkablefeatures, i.e., which, in X-ray exposure using synchrotron radiationhaving the maximum light intensity of light entering a mask portion at awavelength of 0.6 to 1 nm, can decrease the thickness of an X-rayabsorber by the use of an X-ray absorber material having largeabsorption in that exposure wavelength region, and can improve theresolution of a pattern-transfer by the use of a material whose phaseshift is controlled, a method of manufacturing the same, an X-rayexposure apparatus, and an X-ray exposure method.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and representative embodiments shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

What is claimed is:
 1. An X-ray exposure method comprising: supportingan X-ray mask unit in which a patterned X-ray absorber is formed on amembrane, said patterned X-ray absorber containing one of an elementhaving a density/atomic weight of not less than 0.085 [g/cm³] and anL-shell absorption edge at a wavelength of 0.75 to 1.6 nm and an elementhaving a density/atomic weight of not less than 0.04 [g/cm³] and anM-shell absorption edge at a wavelength of 0.75 to 1.6 nm; and applyingsynchrotron radiation having maximum light intensity at a wavelength of0.6 to 1 nm onto said X-ray mask unit.
 2. A method according to claim 1,wherein said patterned X-ray absorber is a material containing at leastone element selected from the group of Co, Ni, Cu, Zn, Ga, La, Ce, Pr,Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu.
 3. A methodaccording to claim 1, wherein said patterned X-ray absorber is amaterial containing at least one element selected from the group of Cu,Ni, and Zn.
 4. A method according to claim 1, wherein a patternedtransparent film different from the patterned X-ray absorber is furtherformed on said membrane.
 5. A method according to claim 4, wherein saidpatterned transparent film is a material containing at least oneselected from the group of SiO₂, SiC, Si, SrO, and SiON.
 6. An X-rayexposure method comprising: supporting an X-ray mask unit in which apatterned X-ray absorber is formed on a membrane, said patterned X-rayabsorber being formed of one of an alloy and a multi-layer film, whichcomprises a first material containing an element having an L-shellabsorption edge or an M-shell absorption edge at a wavelength of 0.75 to1.6 nm and a second material containing an element having an M-shellabsorption edge at a wavelength of 0.5 to 0.75 nm; and applyingsynchrotron radiation having maximum light intensity at a wavelength of0.6 to 1 nm onto said X-ray mask unit.
 7. A method according to claim 6,wherein said first material contains at least one element selected fromthe group of lanthanoid rare-earth elements of atomic numbers 57 to 71and, Co, Ni, Cu, Zn, and Ga, and said second material contains at leastone element selected from the group of Hf, Ta, W, Re, Os, Ir, Pt, Au,and Hg of atomic numbers 72 to
 80. 8. A method according to claim 6,wherein a patterned transparent film different from the patterned X-rayabsorber is further formed on said membrane.
 9. A method according toclaim 8, wherein said patterned transparent film is a materialcontaining at least one element selected from the group of SiO₂, SiC,Si, SrO, and SION.
 10. An X-ray exposure method comprising: supportingan X-ray mask unit in which a patterned X-ray absorber is formed on amembrane, said patterned X-ray absorber being a material containing as amajor constituent an element having all L- and M-shell absorption edgesin a region shorter than the shortest wavelength or longer than thelongest wavelength of an exposure wavelength region having an intensitynot less than {fraction (1/10)} the light intensity at a wavelength ofmaximum light intensity of synchrotron radiation to be incident; andapplying the synchrotron radiation onto said X-ray mask unit.
 11. Amethod according to claim 10, wherein the synchrotron radiation hasmaximum light intensity at a wavelength of 0.6 to 1 nm, and all the L-and M-shell absorption edges of the element exist in a region of notmore than 0.65 nm and not less than 1.02 nm.
 12. A method according toclaim 11, wherein said patterned X-ray absorber is a material containingas a major constituent at least one element selected from the group ofTi, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, La,Ce, Pr, Nd, Pm, Sm, Eu, and Gd.
 13. A method according to claim 11,wherein said patterned X-ray absorber is a material containing as amajor constituent at least one element selected from the group of Cu,Ni, and Zn.
 14. A method according to claim 10, wherein a patternedtransparent film different from the patterned X-ray absorber is furtherformed on said membrane.
 15. A method according to claim 14, whereinsaid patterned transparent film is a material containing at least oneelement selected from the group of SiO₂, SiC, Si, SrO, and SiON.
 16. Amethod according to claim 14, wherein a material, which makes the ratioof a deviation of maximum an minimum phase shift difference between theabsorber and the transparent material with arbitrary thickness for thewavelength of the exposure wavelength from an average phase shiftdifference in the exposure wavelength region smaller than that of adeviation of maximum and minimum phase shift of the absorber witharbitrary thickness for the wavelength of the exposure wavelength froman average phase shift difference in the exposure wavelength region, isused as the material of said transparent film.